The T6 is Canon's most entry-level DSLR... and currently is being phased out and superseded by the T7 which has just been announced. As a result, there's some discounting of T6 to clear the shelves in stores.
I suppose it's a testament to the success of the T6 that the T7 is almost identical. The only changes appear to be a higher resolution sensor: 24MP in T7 versus 18MP in the T6.
One thing I don't care for is that the T6 (and T7) DON'T HAVE a self-cleaning sensor. I often have to shoot in dusty conditions and prior to using cameras with self-cleaning sensors, I had to do manual cleanings every one to 3 months. Now using Canon with self-cleaning sensors it's more like once a year or so, that a manual cleaning is needed. The T6 and T7 are the ONLY Canon DSLRs without this feature that I feel is very useful. (In fact I passed over buying the original 5D full frame model because it also didn't have a self-cleaning sensor and had a bit of a reputation as a "dust magnet". I waited and bought a 5D Mark II with the self-cleaning... don't use it nearly as much as my APS-C cameras or in as dusty conditions... and I think I may have manually cleaned it once or twice in 7 years).
The EOS Rebel T6 (called EOS 1300D elsewhere in the world and EOS "Kiss" X80 in Japan) is relatively small and light weight. (The Rebel SL2/200D is smaller/lighter, but has more features and costs a little more.)
T6 has a lot of automation... sort of like a point-n-shoot that allows interchangeable lenses. That makes sense, since it's likely that a lot of T6 buyers are stepping up from a P&S camera to their first DSLR.
T6 is often found "in kit" with one or more lenses. The EF-S 18-55mm IS "II" that it's usually fitted with is okay... but it's a micro motor lens. I'd prefer the EF-S 18-55mm IS "STM" for it's faster/quieter "stepper motor" autofocus, but it's a fairly minor difference.
More important is if you buy the two lens kit, be certain to get the EF-S 55-250mm IS STM telephoto zoom... NOT the cheaper EF
75-300mm "III". The latter is Canon's cheapest tele zoom and acts the part. The 75-300 III lacks IS (image stabilization), has slower/noisier micro motor focus drive (more of an issue on a tele zoom, than the 18-55mm) AND it simply doesn't have all that great image quality.... especially toward the 300mm end of its zoom range, which is likely what you'd want it for.
The EF-S 55-250mm IS STM is a better lens in pretty much all respects. It's got better image quality and is able to focus closer, it has faster/quieter STM focus drive, and it has helpful IS. IMO, it's worth the additional cost.
Don't confuse the T6 with the T6i or T6s, both of which are more advanced cameras with a number of additional features (also now superseded by newer models: T7i and 77D, respectively).
Incidentally, if you prefer a smaller camera, the Rebel SL1 is still widely available new and is similar to the T6, but comes fitted with the EF-S 18-55mm IS STM lens mentioned above. It does not appear to be offered in kit with 55-250 though... only with that 75-300mm III. So I'd recommend not buying it in the two lens kit. Instead get it only with the 18-55mm and add the tele zoom of your choice separately.
Besides being offered with the slightly better 18-55mm lens, the 18MP SL1 also has a self-cleaning sensor, a Touch Screen rear monitor (fixed) and faster continuous shooting rate.
The SL2 got an upgrade to 24MP and it's Touch Screen is articulated. The SL2 also has Dual Pixel Auto Focus (DPAF) in Live View mode, which is much faster than the earlier forms of AF used in Live View and helps make it much more usable.
Both the SL1 and SL2 use newer processors (Digic 5 and Digic 7, respectively) that allow them to shoot continuously at higher frame rates than the T6/T7... The SL1 can shoot at 4 frames per second and the SL2 at 5 fps. The T6 & T7 both use Digic 4 processors and are limited to 3 fps.
T6's and T7's ISO range is 100-6400 (extends to 12800). The SL1's range is 100-12800 (extends to 25600) and the SL2's is 100-25600 (extends to 51200).
All these Canon are a lot more similar than they're different. I do feel the 24MP cameras offer a noticeable step up from the older 18MP in a number of ways... overall better image quality, increased dynamic range, higher usable ISO (allowing shooting in lower light conditions).
One place the T6, T7, SL1 and SL2 are all virtually identical is their optical viewfinders and the autofocus system you'll see there. Like all Rebel series models, they all use a "penta-mirror" instead of a pentaprism, to save weight and cost. They also are all 95% viewfinders with around .85X magnification (some of the more advanced cameras have bigger, brighter 100% viewfinders with up to 1.0X magnification). And all four models use a similar, fairly simple and easy to use 9-point AF system that has one higher performance "cross type" AF point at the center (the more advanced Canon DSLRs have far more complex 45, 61 or 65-point systems, most of which are all cross type).
T6, T7, SL1 and SL2 all also use the same SD type memory cards. The T6 and T7 use the same LP-E10 battery, while the , in each typeSL1 and SL2 use LP-E12 and LP-E17, respectively. The T6 and (I think) T7 can optionally be fitted with a vertical/battery grip.... doubling the number of batteries and providing convenient, vertical controls (2nd shutter release button, etc.) The SL1 and SL2 cannot be fitted with a battery grip, probably because they are intended to be the smallest APS-C DSLRs available.
To summarize, here's the current Canon USA interchangeable lens camera line-up from most entry-level to most advanced:
DSLRs, APS-C size sensors (EF-S and EF lenses):
EOS Rebel T6... 18MP, 9-point AF, discontinued.
EOS Rebel T7... 24MP, 9-point AF, new, announced but not in stores yet.
EOS Rebel SL1... 18MP, 9-point AF, discontinued.
EOS Rebel S2... 24MP, 9-point AF, new, in stores now.
EOS Rebel T6i... 18MP, 19-point AF, discontinued.
EOS Rebel T7i... 24MP, 45-point AF
EOS Rebel T6s... 18MP, 19-point AF, discontinued.
EOS 77D.......... 24MP, 45-point AF (replaces T6s, in spite of not being called a Rebel)
EOS 80D.......... 24MP, 45-point AF, 7 fps, higher spec shutter, pentaprism & more
EOS 7D Mk II... 20 MP, 65-point AF, 10 fps, magnesium body, higher spec shutter & more.
DSLRs with "full frame" sensors (EF lenses):
EOS 6D........... 20MP, discontinued
EOS 6D Mk II... 26MP
EOS 5D Mk III.. 22MP, discontinued
EOS 5D Mk IV.. 30MP
EOS 5Ds.......... 50MP, low pass filter
EOS 5Ds-R...... 50MP, no low pass filter
EOS DX Mk II.. 20MP
Mirrorless, all with APS-C size sensors (EF-M lenses, w/adapter EF-S & EF lenses):
EOS M100... 24MP, no viewfinder
EOS M50..... 24MP, electronic viewfinder
EOS M6...... 24MP, no viewfinder
EOS M5...... 24MP, electronic viewfinder
For more info on any of the abovve, I recommend Brian Carnathan's website with very thorough reviews and comparisons.
https://www.the-digital-picture.com/Reviews/Canon-EOS-Rebel-SL2.aspxHope this helps! Have fun shopping.