Cheapest is to have the stock head recut and milled, drop in a new crank, sell the bad one, bore, hone and piston kit.
Next option same as above with noss head. Then you can go higher on compression if you want some more bottom end and decide to use race gas.
Fastest option, new stroker crank, porting, carbs, airbox mod or pod filters, clutch very soon, noss head, sell the bad crank, bore, hone and piston kit.