Thought it was a head gasket, turned out to be a grenaded piston :(

I picked up a non-running 2007 Tank Vision 250 with a copycat Honda CA250 253FMM 250/300 Twin 4T engine for $180 the other day, previous owner said it'd just blown a head gasket and he didn't have the time or skill to fix it. Sweet deal for a titled frame with mostly intact running gear, let alone with a relatively easy engine fix I says to myself. Well... I got the engine dropped out last night, and here's what I found:

http://i.imgur.com/VML6H0u.jpg

http://i.imgur.com/H4o76F2.jpg

http://i.imgur.com/padOn46.jpg

Busted piston, seized rings on that side, scarred cylinder, bent valves, scarred cam shaft mounting channels, and a cam shaft that's lobes are about 1/8" shorter than they should be with a lot of cooked-on grease. I know the cylinder and top end are a total loss, but the guy said he was able to ride it for several miles back to his house when the engine took a dump (likely causing most of this damage I know).

What I'm wondering now is where/if I can get a whole new crate motor for this bike for less than the cost of repairing it, and what the likelihood of the bottom end being okay still is. As far as I can tell everything shifts and spins freely in the bottom end. If it were a GY6 scooter I'd know in an instant which is the better route, but I'm not sure with this motor. Unfortunately there's no donor Rebels or NightHawk's to rob an engine from in my area either.

Any advice?