There are alot of fish you can add!!!
Based on your limited money supply however, you I'm guessing won't want to blow a grand or so on equipment for the tank, and thats fine--just pick some of the hardier species like triggers and keep your load very,very low. In my opinion you can have a great tank even on a limited budget. (although I know alot of people will disagree)If you just accept that your capabilities and choices are limited as well. Me, I'd put a great big fat trigger and a great big fat naso tang and call it good. Very hardy, very entertaining, and colorful too. No need for the top notch stuff or all the hassle, headaches, and dissapointments that come with keeping the
more delicate stuff.
Good Luck