Exactly what does it mean to "shred and bust air"?
I have a 10' inflatable with a hard bottom and a 9.9 HP outboard that will do 22 MPH. I actually use it to pull wakeboarders past the slider.
Video of it is here: http://rodm7.tripod.com/
The boat is somewhat portable: Take the motor off and two guys can lift it on top of a large SUV.
I think you will be pretty hard pressed to find a useable inflatable and motor for under $500. A package like that new would be around $5000.
You can often pick up some 20 year old Jet Skiis for under $500, including a trailer!