Have you considered a Honda 400EX? Parts are dirt cheap, the quads arent expensive, and they are stupid reliable. Also really easy to work on. They make great trail rides. Put a little money into the suspension and motor, and you will have a dead reliable quad that can tackle just about any trail and you can have some fun on the track as well. worried about getting bored with the speed? increase the bore size and you can get a lot of power out of them for the price and amount of money you spend. just sayin...
~Beefy~
-2001 400EX: 450R shocks, Renthal bars, AC Racing nerfs, MSR AOF Clutch Lever, K&N with Outerwears , CCP Steering Stabilizer, Old school Big Gun Exhaust, PRM Desert Grab Bar, Rock bumper, Ricochet Swing arm, Skid plate, Pro Grips, Emgo Hand guards, Primary Drive sprockets, GBC Shredder Tires, LSR Parking Brake Delete, N-Style Graphics and GripperSeat
-1998 Polaris Trail Blazer 250 (Dad's): Fox Shocks, ProTaper bars, Badlands 2000lb winch