OK, thanks. I've seen it now... and although the cause isn't yet obvious, you may be in with a chance of salvaging what you have.
It looks as if something held one of the inlets open, which bent the valve, which smashed the valve guide. What held the valve open in the first place isn't clear. I don't understand the damage to the top of the valve stem where the shim is supposed to sit either, and I suspect that had something to do with it. I'm guessing maybe the valve collets escaped? I think I'd be asking the previous owner exactly what he did to the bike before you bought it. Not because I think he's liable in any way (and that's your business anyway), but to try and understand what started the whole chain of events that led you to here.
Anyway, pull the cylinder and carefully check the piston top ring land. Hopefully there's no cracking or damage. If the top ring is trapped, you may be able to recover the piston, but I would never trust it not to be cracked, and I'd always expect it to let go at a future time. If the top ring is free, file off the worst of the scabs on the piston crown and re-use it.
Strip the head and see if the surface of the combustion chamber can be recovered and look for other damage, such as to the valve seat. If most of the scabs and embedded junk can be removed, it's probably worth the effort of replacing that one valve guide and valve to see if you can get it running. I recommend replacing the valve spring and spring retainers on that valve too. Is the cam, rocker arm and follower bearing OK?
It really depends on what more you find when you dig deeper. It's not a perfect solution, but it should get you back on the trails without huge expense... and you could always replace the head when you've a little more cash.
On a final point, what's the price of a used replacement engine? If you're expecting to spend over 2000$ on rebuilding the beast, what's the price of a heart transplant?
Good luck!
Cheers... Paul