Apart from crash damage, probably the #1 expensive problem to be aware of is worn dogs on 2nd gear. Under hard throttle, the bike will pop-out of gear. Engine out of the frame, cases split to fix, at-least one gearset, and since it's open, the shift drum and shift forks, assuming you're keeping it. If you cannot do this work yourself, the cost at a reputable shop will unfortunately exceed the value of the bike in most cases, since the bike probably has a bunch of parts replacement it needs: tires, brake pads; bleeding and rebuilding of the master cylinders (rebuilt or replaced), a good battery, carburetors rebuilt; fork seals replacement, or replacement of fork downtubes because of rust; steering head bearings, seat covers, etc. You get the picture. Fortunately, pretty-much everything is still available new or used.
I wouldn't pay-over parts-bike prices for anything which wouldn't start and run, with a demonstration of 2nd gear being intact. It has to have a title, too, it costs too-much to get a title for a bike without one, after checking the insurance company registry and the NCIC computer system for stolen bikes.
Pay $1800 for a bike, "it just needs a new battery," and come to find-out, the carbs need disassembly, cleaning, and rebuilding, and once it's able to start, you discover 2nd gear is bad, to begin, plus the parts named above, due to being used-up and not maintained. Good luck finding a Yamaha dealer even willing to do that case-split repair, because the owners often abandon the bike once they get that $2,000+ bill. If you have skills to fix a bad 2nd gear, your options are increased.
My non-runner
top-price is about $500, depending upon the condition of the bike overall and its accessories. A disassembled, roached-out bike, < 1/2 of that.
I once answered an ad for a "V-4 Yamaha", he wasn't asking much for it, but when I saw the bike it was debatable if I would take it, if he
gave-it to me! It was stored outside, the carbs were off, and there were mosquito larvae in the standing water which filled the intake runners. No paperwork with it. He was losing his storage space, it had to-go, but he was adamant that it had value. Not to-me! I kept my eye on the storage yard, and one day I saw a roll-off dumpster and a big front-end loader scrapping everything in the yard.
Here's a good thread to read:
New Vmax Owner FAQs....new members please read!