how much would it cost to replace a heater core in a 71 cutlass

If repair shop can fine one or replace with a re-built one that would work - probably some $300-$400.

probably around 175-300 depending on if its got air conditioning on it or not,and that would be counting the cost of the heater core,their not that bad to do on those cars,good luck.

Year one sells them for $95.95 plus shipping. Do not buy a rebuilt one. New are not much more and are better. The labor will depend on how hard it is to access. Many GM cars of that era had a pretty simple replacement process.

45-60 dollars
i just a new heater core in my cutlass