skip the drift tires and focus more on a new engine. Ok at least look for a new engine online. Theres been a few .18ss go for 80 something on ebay..... speaking of witch

http://cgi.ebay.com/NIB-HPI-15FE-Red...QQcmdZViewItem

THERE! THATS THE BEST UPGRADE FOR YOUR .15fe ENGINE!!! This seller has a few different colors and it will help keep u in budget. But i mean u can get a new exhaust for around $40-45 so it woulnd't hurt to look