With what system do you propose doing this?
Modern electronically controlled lenses cannot be used in reverse (well, to be accurate, it might be possible... but typically isn't cheap or easy).
If you want to do reverse lens macro, you would be best getting a vintage lens that has a built-in mechanical control for the lens aperture. Usually that's a ring at the base of the lens that you twist to set to different lens apertures. I'd recommend a lens in the 50 to 135mm range of focal lengths.
You then will need to find a reversing ring that fits the lens' filter threads.
This will not have any electronic contacts to communicate with the camera, so you may need to set something in the camera's menu. Often they are designed to not trip the shutter when there is no lens installed, to prevent accidents. In one of my cameras, I had to "enable" a feature labelled "allow shutter to fire without lens". Check your manual or scroll through the camera's menu to see if you find something similar.
With this type of lens, you will have limited usable exposure modes. You cannot use any exposure mode where the camera would normally need to change the lens aperture. Of course you can use fully manual exposure, where you choose the shutter speed, lens aperture (set on the lens, now) and the ISO. You also can probably use "aperture priority" auto exposure. Here you choose the aperture (on the lens) and the ISO (in the camera), and leave it to the camera to select the shutter speed that it thinks will make a "correct" exposure. Assuming your camera has it, you also can use Auto ISO with M, which is another form of auto exposure. In this case you choose the aperture (on the lens), the shutter speed (in the camera) and the camera will choose an ISO that it thinks will make a correct exposure.
DO NOT use P (program) or shutter priority AE (S on Nikon, Sony & others or Tv on Canon). In both of these AE modes the camera needs to be able to adjust the aperture, which it cannot do with the reversed lens.
Also DO NOT use any "scene" modes like "sports", "landscape", "portrait", etc. And DON'T use the full "Auto" (point n shoot) mode, if your camera has it.
One problem with reversed lenses is that it can be difficult to shade the rear element (not the front element) of the lens from oblique light and it may not have anti-reflective coatings like the front element of many lenses have. On one lens, I solved this problem by using a rear lens cap, modified into a "lens hood" by removing the center of it completely.
Another possible problem is that some lenses have little buttons or levers that are moved to release the lens aperture only when the lens is mounted on a camera. Canon's earlier "FD" mount lenses "park" their aperture at f/5.6 when they are removed from the camera and there is no way to change it. There's a little tab or lever hiding in the mount that needs to be pressed to allow the aperture to be changed manually. When the lens is on a camera, no problemo... that little tab or lever is actuated and the lens works normally. A solution in this case was a special "rear lens cap" provided by Canon to repair techs, needed whenever they were working on FD lenses. It also is open on the bottom, so can serve as a hood on a reversed lens too. I was lucky to get one of these some years ago. They're quite rare!
Most other lens systems I'm aware of aren't a problem, but I'm certainly not familiar with all of them! I know Nikon F, Konica K/AR, Minolta MC and MD, Pentax screwmount and PK bayonet, and Olympus lenses are fine.
Another technique for macro on the cheap was to reverse mount one lens on another. It's most easily done when they have the same filter thread. At one time I used a 135mm lens and reversed a 28mm in front of it. If I recall correctly, they both used 55mm filters, so it was just a matter of getting a "reverse stacking" adapter that allowed them to screw together. The 28mm lens acted like a high quality "diopter" on the front of the 135mm.
I don't do any reversing or reverse stacking now. Both methods have a lot of limitations and are a bit of a pain, especially trying to do them on modern cameras. It made sense back in the days of film, when we could do both with lenses already in our camera bags. Today you pretty much have to buy a special lens or two, in order to use these techniques.
Much easier to just get a high quality diopter lens or, even better, a set of macro extension tubes. I have one diopter for use on one lens.... and several sets of extension tubes for use with virtually any lens ever made for my cameras. I always have some extension tubes with me. I occasionally get out the diopter for use with that one particular lens. High quality diopters ain't cheap. This one sold for around $140. That's a lot to spend to only use it on one lens! (I thought I'd use it on more, but there's some loss of image quality, even with a top of the line diopter).
If you consider macro extension tubes, the OEM tubes sold by the camera makers are very pricey, often sold individually or don't work with every lens. There are very good third party such as the Kenko ($130 for a set of three: 12mm, 20mm, 36mm that can be used singly or combined with each other). Nearly as good are similar sets offered by Viltrox, Opteka, Vello, Fotodiox and a few others (around $75). In some cases, those same manufacturers offer less expensive, more plasticky "economy" versions (around $50). I suppose those would be okay with really lightweight lenses and cameras, but I think it might be a lot better to spend a little more for the "better" ones.
AVOID the really cheap macro extension tubes... under $25... sometimes even less than $15 or under $10! These are "dumb" tubes without the electronic connections for the lens and camera to communicate. They simply won't work with many modern lenses... Or you have to do all sorts of complex work-arounds to use them. Not worth the savings.
If just starting out shooting macro on a tight budget, I might recommend looking for a vintage manual focus lens. There are lots of them around and sometimes they can be had pretty cheaply.
I picked up a Tamron SP 90mm f/2.5 lens from the 1980s at a local secondhand store for all of $20. It was in great shape with the original caps, lens hood and a matched "doubler". It is one of a number of interchangeable "Adaptall" mount lens Tamron sold in those days. The "SP" line were generally their best and most pro-oriented. Mine came with a Nikon F-mount on it, but I needed to fit it to a modern Canon camera. Turns out, Adaptall mounts are still being made for just about every camera system, so I ordered one from China. It cost $40, including shipping, and arrived in 4 days. It's a "chipped" adapter that sort of communicates with the camera (just lets it know there's a lens mounted, to avoid the problem mentioned above)... there are cheaper ones without the chip (about $25 or $30). $60 for a good macro lens, not bad! It's strictly manual (aperture and focus), so slower to work with. But works fine. (More recently I've adapted if for use on a mirrorless camera. There's an Adaptall for that, too! I have them for a bunch of different camera systems).
My $60 Tamron SP 90mm only does 1:2 or half life size on it's own... so for this shot I added a 20mm Kenko macro extension tube behind it....
These two shots of poppy buds show the difference between the lens with the 20mm extension tube and without it...
Here's the Tamron 90mm mounted on one of my DSLRs.... Alongside is an image showing the compact lens off the camera, with F-mount Adaptall next to it.... And the third images shows the lens along with some macro extension tubes...