I am looking to get my 5 (soon to be 6) year old a BMX bike for dirt track/ramp racing. He is a little guy (43", 36lbs) so I don't want a bike that weighs as much as he does. I have seen some "Minis" that weigh 15lbs from Redline. Are there other good possibilities that are 20" rim bikes for a beginner racer? I'd prefer not to spend more than $300 but give me all suggestions in case I find a deal out there. Thanks!