They are very accurate for a surplus rifle. You should see decent results out to 200 yards - easy. However, mounting a scope requires a special mount. I have not heard how well these mounts work.
I doubt that the typical k-31 will hang with the typical Rem 700. It would depend on the specific gun and shooter. My k-31 will not hang with my varmint model Rem 700, but I would not expect it too. Still, I love the K-31.
The price you mentioned for the rifle seems very good. However, Ammo is not as cheap as other surplus though. Walnut stocks and matching numbers both add value.
Summary, buy it; you won't regret it.