Heater core replacement questions/cost

I have an 05 Passat with the 2.0 diesel, and last winter I ran into a bit of a problem; I had no heat, what-so-ever.
After some researcher I figured out that it was the heater core. Since there was about a foot of snow on the ground and I have no garage I did a quick flush and got maybe 20-30% heat back. Im gonna try and do a more thorough flush before winter comes, but if it doesn't work well enough I may be in the market for a heater core replacement.
So my question is what would be the estimated cost for a heater core replacement including parts and labor?
I know Munks is close to me and I believe Steves European Auto is as well. Any input would be greatly appreciated and if you've had any experience at either of those places I would love yo hear it.
Thank you

I've had luck using CLR. Fill up the core, both ends removed so not to get it in the rest of the engine. Let is sit overnight and flush and backflush it. Also, when filling it make sure it's bled, done so by filling the block etc and having the hoses pulled back on the nipples exposing the bleed holes in the hoses.