I agree totally on *cheap* 2000# winches, but you can get good quality trailer winches new for a lot less than a used 8000#. An 8000# winch is probably overkill, and can be alot of work to install on a trailer, especialy when you consider those things pull over 400 amps at full load.
I was suggesting an 8000 lb winch cause it will pull about anything you could haul on a car trailer. A smaller winch would probaly work but eventually you will get a car that is non rolling or missing suspension parts and you will have to drag it. A small winch would probaly work but it would be a load. I have seen 8000 lb superwinches for around $500 new.
Superwinch 4000 in enclosed trailer,,works great, really need it with new car, door hits wheel well, lexan windows of the nonworking type, Winch the roller on an off. No junk picking with the trailer
My first winch I bought was a $39 from harbor like Ricks. I loaded several cars with it, Including my wifes Explorer up hill in a parking lot. (granted it took 45 minutes) I still have that winch and it still works . 3 years ago I bought a 8000# winch from harbor I have abused the crap out of it and it's still ticking the price on it was $300. I haul alot of junk cars to the crusher 20-30 a year so I feel I've givin it good test.
i have a 3500 superwinch in my enclosed trailer. does great. previous owner of my trailer had a 67 pontiac tempest that weighed 3400 lbs. and the winch did fine.
if you get non-rollers on the trailer all you need to get them off is a chain and a big tree. Back up chain the car to the tree and drive off. the cheapest to get it off