You may want to consider looking for a used engine. For sure you're looking at a gasket set, valves and piston plus possible valve seat or cylinder wall damage, a bent connecting rod and twisted crankshaft. Plus there was a reason for the valves hitting the piston in the first place. If it wasn't from over-reving, then there must have been a problem with the cam chain, cam chain tensioner or cam chain guides. You might tear things down first and take stock of what you have to work with before you go to buying parts.
