Would you find it fun to work on it for several months to get it up and running? If that sounds like a great time then I would go for it. If you aren't too interested, then don't do it.
Also, you'll likely have to spend some extra cash in parts to get it running, possibly as much as $2K, or as little as ~$400 depending on what is wrong with it.
If you want the lowest possible cost bike, get something that is running (and make sure you have enough left over to invest in new tires, proper riding gear and insurance).
1981 CB750K with 900 cams
90K KM's, rebuilt head, rebuilt carbs, upgraded valve stem seals
My wife's recipe website that I'm trying to help promote:
Strawberries for supper. Yes, I am a lucky man.