not hard to get 20 hp outa a west bend 820 .. there 134cc and off the shelf I think there 12hp ..
stone stock blueprinted with alky carb get you 15 + all day easy ..
9 ported cut flywheel thin ring piston good rod bolts decked block full circle crank stuffed and duel alky carbs .. worth 10,000 to 12,000 rpm and easy 25 - 28 hp ..
5000.00 would still be a little rich for me ... but ill bet it would cost nearly that to build one just like it ..