You should look at electric shift kits from sickbikeparts. It requires a battery and bms, but in the end you would be paying less in maintenece and gas. You could even put it on a full suspension bicycle. Ive built a 2-Stroke bike from the ground up on a skyhawk frame and the final cost for me was about $1,200 and took me about a year on and off.
My next build will be an electric 1000w+ 30 - 50 mile range on a full suspention frame.