save yer money and buy an older bike to mod or one that is already in that style. If you really have the 300 in your sights and money/time to burn then make sure you post pics!
Seriously though, to do it right would probably require a bit of custom modification and headaches. A lot of sport bikes that I see people try and transition on their own end up looking sorta shoddy. I personally have always like the looks of an old Honda CB500 cafe'd the fuck out. I know its not the same as 'streetfighter' but the older CBs are cheap to buy, maintain, mod and much easier to have them turn out looking original and good.
Here's a link I found to a guy in a forum that did his '08 ninja 250. It can give you an idea of what it might end up like...
http://www.customfighters.com/forums/showthread.php?t=22780