[lincpimp]

I would not waste any money on a better brushed motor...

If you pick up a decent 2s lipo, it will make quite an improvement with the stock traxxas xl5 esc and titan 12t. You will need a low voltage cutoff, like a li-saver, or novak smart stop.

Keep in mind that you can sell the xl5 esc and titan... Might get 30-40 bucks.

Used sidewinders are easy to find, I got 3 of them one week for 50 bucks each. The medusa suggested is a good motor, but you can find used vxl motors pretty cheap, and used cc motors can be had cheap too. It all depends how budget you want to go. At 35 bucks a month, you may just want to play with what you have. That would barely cover my breakage costs...