BB is an idea...
You could also consider a good tool kit for the back. I know its not a performance mod, but it can never be overrated. I bought a collapsable crate from Target ($7) then went to Wally world and bought a cheap 60 pc automotive repair kit ($20), threw in a few quarts of fluids - (Gear oil, brake fluid, ATF, and the standard 30W motor oil) a tire patch kit ($5) some rubber gloves, shop rags, a funnel, flashlight, and a roll of duct tape. There you go, for about fifty bucks, you've got your basic trail tool kit. I must say its saved my arse more than a few times!
More performance, I guess you could peice together a better exhaust with $75 bucks a month or so...
I'll leave it at that, hope this helps.
Hank