By all accounts it looks to be in very good shape. Main thing about M39's I've seen over the years is their bore sizes vary a bit. Mosin's are supposed to be .311 diameter but some Finnish rifles are .308 and .310 and etc. They are considered to be the cream of the crop as far as Mosin's go save for maybe a true arsenal built sniper model. That said, they are still a Mosin, so $600-$700 is what I see them run at. Some go for more but I think it's wishful thinking on the sellers part.
If it's worth it to you, go ahead and buy it. Ammo is still plenty cheap and available.