the trouble with going downhill, is it can be hard to stop...........

Since you're only going straight back it'll be easier to move it on its own wheels then with wheel dollies.
If you're slipping on the floor put your hands on top If one of the tires and try rotating it that way and it'll make it move. Make sure you're not in park or gear of course.

Back when I lived in a condo I had a one car garage but room on one side for another car but it wasn't accessible via the garage door . I used to put my Dart or one of the project cars I had there , I just jacked the car up front or back and move it with my floor jack and push the car , it only took a few shots with the jack to get the car in place, Dollies sure would have been easier if I had them back then.

I traded a friend for these Dolly set
He is not a car guy and got them from his father in law's estate I gave him some ammo for it.
They work great , easy to push cars around and put in the corner.

those seem to be a top tier dolly set, and if i really needed a set to use very frequently, i would seriously be considering a set of those.

I've got a couple sets of the Harbor Freight version of the "Go Jacks". They work very well for moving a car around on a smooth garage floor. A person can do it pretty effortlessly by themselves! But it sounds like you need to climb up an inclined apron to your garage. These roll movers are not cheap but are very effective for moving VERY heavy rolls or spools (or heavy vehicles on wheels) They are available in electric and pneumatic versions. I used these in my years of paper making (large heavy paper rolls) perhaps you could search for a used one in your area for cheaper. Just thought I would share another potential solution to your problem since it hadn't been mentioned. Car/roll mover

another linky to pusher

So what does one of these cost? I'm afraid it's another one of those, if you have to ask how much it costs, you can't afford it.

My previous house had an incline just outside the garage. I would jack up my truck and put 2x4s under the front tires and push it off those into the garage. It was much easier than pushing it up the incline.

Ya! I'm not sure what they cost...... I'm sure they are pretty spendy, being used in industry! They seem to nick industry pretty hard due to liability issues and the fact that ADA laws can require tools like this to accommodate employees unable to perform certain tasks. I see a used one on eBay missing the handle for $750