so its essentially a kit you can get for the Aprillia SXV 450 or 550, you can also use these on 450 mx bikes from KTM, Yamaha, Kawi etc. but the Aprillia 550 is the one that has a v twin engine better suited for street riding/racing. so depending on how much money you spend, you can get a bike with 70 hp that's under 300 lbs.
the kits arent cheap though, but you might save money finding individual parts on your own. here's some links below for a good read about these.