A boost activated pressure source is easy and has been done. You just need a boost switch that activates a secondary fuel pump or increases voltage of the existing pump at a certain psi.
I don't think you'll make a supercharger for that low of a cost. Only ones that cost that low are high production models. you're better off buying one that's already made for motorcycles. I found a company in the UK called Rotrex.
http://www.rotrex.com/Home/Superchar...torcycles.aspx. The only thing is that it seems the dimensions for it may make keeping the fairings in tact really difficult.