Some good 1990's titles but will be hard to find for $600-$800 unless it's ready a project machine.
Some of the 'A' title 1980's games are getting hard to find for that price range. You many want to up your price range by $200+.
Popular 1980's titles that you should be able to find for $600-$1000 (depending on condition): Xenon, 8-Ball Deluxe, Centaur, Firepower, Blackout, Black Knight, Pharaoh, Solar Fire, Barracora, Comet, High Speed, Pinbot, F14.
Games like : BK2000, Taxi, Earthshaker, Whirlwind, Diner, Banazi Run, Cyclone are getting very hard to find for under $1000 or even $1200 these days.
Condition is everything: A game with a backglass that is extremely nice may up the price $100-$200. Games with better than average playfields, clean electronics, nice cabinets, etc will all add value to a game.
Just don't buy a cheap pin because of the price. Play it. Games like Gensis, Raven, Spring Break, Hardbody, etc are usually cheap for a reason. While some people may like these games they are usually found to have a poor replay value.