O-320 Engine Costs - 172

As I've been discussing in another thread, I'm evaluating a 1982 C172P
for purchase. I was using $20k as the TOTAL cost of an engine
replacement, but apparently that is high.

I'd like to hear from owners that have experience with this. If I
take it in at 2000 hrs, what am I going to pay (read: how much will
the check be) to get to 0 SMOH? I presume there are variables, like
having an annual done at the same time, helping with the swap, etc.
For budgeting and negotiating purposes, though, what should I figure
on to get it back to 0 time?

Thanks all!