Hello Casca-1,
I own 6 Ruger #1s in different calibers,but none of them are a 22-250 cal.
If the gun is in good to excellent shape then you should buy it,but offer him $650.no more.
You can check out other gun sites for prices on the same rifle.
Try, Guns America
Guns International
Gun Broker
I have found 2 really mint Rugers on there for great prices.They were Diamonds in the rough.
Good Luck