Got this off of eBay for $25, I would love to start modding it so where do I start?

No matter what your budget is get a decent soldering iron. When I first started modding flywheelers, a basic rewire was a good start, just removing the locks pretty much (this is dead easy on the Stryfe, only three wires + motor bridges!). I think you can put Honeybadger motors in it while keeping the AAs too, but later on you can get into higher performance with a LiPO or NiMH.