here is a novak system for 150.
http://www3.towerhobbies.com/cgi-bin...&I=LXWLX0&P=ML
Im not sure how good of a system you are looking for. I mean very competitive or just something to meet class specs and your son could race with?
When I first got into rc and wanted to go brushless I went with a cheap ESC and a pretty good motor.
here is the ESC:
http://hobbyking.com/hobbyking/store...idProduct=7188
Its not the best ESC on the market but it worked all last season with no problems. It has good programmable options so you can tune it to your liking. Its sensorless but will work on some sensored motors. It will just not be as smooth as a sensored system. I placed 1-3 in many races with it.