The cheapest way to get more out of your bike is the age old solution of throwing your road legal can away and fitting a race one instead; get the carb re-jetted (using either a Dynojet or factory kit), fit a K+N air filter (especially if you own a CCM as the factory filters have no central core to stop the filter deforming at higher RPM and getting sucked towards the carb mouth thus decreasing the air flow when your engine needs it most) and then get the whole thing professionally set-up by a competent mechanic on a dyno. The gains won't be huge, but they will be noticeable - and your bike will sound incredible, too.