i'm just wondering how much does a port polish usually go for on a 350 and where would you go to get this done?

Port and polishing is usually reserved for some serious engine mods. Normally this is done by a speed shop or engine builder. You furnish the heads and manifold and they do the work.

This is usually done in conjunction with a whole lot of other high-buck work which needs to be discussed with the person doing the engine work.

Bob