If you want to try your hand at post processing. Then read on.

Last night was an ok night - "seeing" clouds moving in and out but I took another crack at M31 and have added the file over 400mb to a DropBox folder.

I used the same kit, Nikon D810a, Nikon 200x400 F/4 lens, Atlas Pro mount. Unguided.

I kept:

79 lights (subs) 30 second exposure, F/4, and 2000 ISO - IR UV cut filter and Light Polution Filter added
50 darks
50 bias
50 Flats

All Calibration, Registration, and Debayering was done in Deep Sky Stacker. The result was a file named:

Autosave.fit
or
Autosave.tif

I tried to add it to this message but got the message the file was too large.

If you are interested in seeing what you can do in Post, send me a PM or email with your email address and I will email you a link to Dropbox where you can download the file.

I have not idea if there is much to work with. I plan to work on it later this week when time permits.

My opinion:

for a heavy lens ball heads are a pain, I don't use them

Pan tilt doesn't react fast enough on moving subjects

a gimbal reacts quickly

As to expense, you say 450 - 550

Add $50 and you can get NEST carbon fiber legs and head. Lighter, stronger, less vibration, more weather resistant.

Nest gimbal head $298, 55# load

Nest NT-6324CTM Traveller
Legs w/Monopod $299.00, 44# load and you have a monopod too

This rig will handle anything within reason, and supports enough you can hang a pack or whatever off the bottom for more stability in wind.

If you get a rocket blower, use it in stages.

(1) it should be stored in a box so dust doesn't get into the blower. When you take it out of the box, give the bulb a few squeezes to blow any dust out of the nozzle.

(2) Charge the battery on your camera.

(3) when you take the lens off, hold the camera with the hole facing downwards (so dust won't settle back into the camera) and use the blower to blow out the mirror box (with the mirror down).

(4) Activate the "mirror up for cleaning" menu item and blow out the sensor area. Keep the nozzle out of the camera so it doesn't touch anything.

(5) Check to see if the dust is still there. I find the easiest way to do this is to bring up a blank white page on the word processor on my computer, set the camera to manual focus, set the lens to infinity and a small aperture, put the front of the lens as close to the screen as you can and take a picture. That should give you a fairly uniform gray picture. You may have to blow it up to check for small dust particles. If you see some, go back to step (4)

(6) If the dust is still there after several tries with the blower, it may be dust that is stuck to the sensor. In that case you have to decide whether you want to do a wet cleaning or have someone do it for you. It's not that hard if you have a reasonably steady hand.

Note that you don't want to use a time exposure instead of the "mirror up for cleaning" setting. The sensor is powered up for the time exposure, so static charges may make it hard to get the dust off. The sensor power is turned off for the cleaning setting.