CJs are the "original Jeep" vehicle that eventually became the Wrangler. The last model year for the CJ7 (same dimensions as a Wrangler) was 1986, about the same time Jeep/AMC became part of Chrysler. They have round headlights and a leaf-spring suspension.
YJs were the first-generation Wranglers. They also have a leaf-spring suspension and square headlights. Stay away from the pre-1992 models, they do not have fuel injection and can be unreliable. The last year model for the YJ was 1995.
TJs are the second- and current-generation Wrangler. They have round headlights (bigger than the CJ7's) and a coil-spring suspension. The first year for the TJ was 1997. Most of us here currently drive TJs, though several of us (including myself) used to own YJs or CJs. Jeep owners tend to be lifetime fans because they are very fun and unique vehicles to own, though they do have their quirks.
You are probably looking for a late-model YJ or an early-model TJ, something made between 1994 and 1998, given your budget of 7 to 9 grand. I'd spend some time reading the old posts here--someone who recently bought a Wrangler took a few hours to browse several thousand old posts here and found it to be useful. Wrangler are neat vehicles, but not for everyone.