So you are in OR? I wouldn't pay that kind of $ for that bike from what you described. That's a $1000 bike, maybe $1500 if it runs & has no 2nd gear jumping-out under load issues. Charging issues can be a stator, bad stator wire connection (many people just solder the wires where the plug is, eliminating it), or a bad regulator/rectifier. Or a combo of all 3. You won't know until you look at it.
Not 'on the road?' Have you seen it run? Have you seen it drive/ride? OK, devil's advocate: new stator, new regulator/rectifier, new battery, carb cleaning & some carb replacement parts could easily become a thousand dollar bill at a shop. $1000 for the bike. If he wants to sell it, and hasn't had much interest, he may take your offer. Pray you don't have to split the cases for any reason.