This Yamaha YZ250 was converted into a racer that placed 5th in class at the 2011 Pikes Peak Hill Climb. To make this happen, plenty of custom work was done, including Excel rims, Moto Master brakes, Galfer rotors, and a suspension set up for a 160 pound rider. However, this bike will probably need an engine rebuild, and it includes a new OEM cylinder, Wiseco crank + bearings, gasket kit, and Vertex piston.
As long as you’re willing to rebuild the engine (which you’re going to be doing often enough with a race bike), this is a great base to start racing. Find this Yamaha YZ250 for sale in Petaluma, California for $4,000 here on Bay Area Riders Forum.