I checked on the heater core cost. Slightly under $70.00.
It's easier to replace than the A/C core. Considering you have to remove it to replace the A/C core it goes without saying. It's still a bit of a pain. When you remove the dash, there are a couple bolts under the hood in addition to the obvious ones inside the car. I strongly recommend using some kind of service manual. One of the dash bolts is beside the windshield motor and is hard to get at. The one on the passenger side is pretty easy to take off. When your remove the dash, draw a picture of how the wiring is routed. It will come in handy. You have to drain the coolant. Be sure to us VW coolant when you refill it, the stuff is really good.
The heater core has a couple bolts that go through the firewall and has nuts inside the engine compartment. They aren't too bad to get to, but you do have to climb in a bit.