Dirt Bike Sounds Like Crap When Cruising Down Trails?

I have a kx125 2 stroke bike, I know its meant for racing, but I also like to ride trails. It sounds like it is misfiring at low rpms. So when I am cruising with just a little throttle it sounds choppy, but if i raise the rpms or accelerate it sounds fine. The plug recommended is like $30 and at the rate that 2 stokes foul out I dont want to have to keep buying $30 plugs. Newer cheaper plugs $10 dont help the misfire either though.