TMGP is the cheapest way to get your feet wet in racing. Other than that, your cbr300 would be a good bike. unfortunately you would basically make it unable to ride on the street in order to race it. There is a mini bike race in denton, tx this month. I have some bikes you could ride to get your license and try it out. I'd suggest against going out and buying a new bike before you try it. There are a lot of "start up" expenses to get into racing.