how hard (or how much $ to pay) is it to replace a heater core in a 1999 Pontiac Montanna?

Answer 1

At Auto Zone it runs about $77 for the front one.

Here is the pics and instructions on how to change it. Bookmark for future reference, if you are too cheap to buy a book.
http://www.autozone.com/servlet/UiBroker?ForwardPage=/az/cds/en_us/0900823d/80/1b/e9/79/0900823d801be979.jsp

All you need is a flat tip and phillips screwdriver and a pair of pliers. Also check your hoses BEFORE you take them off so if they show signs of cracks (not the stuff you sell now) you can buy the hose at the parts store and replace it while you are doing the work. Basically, just go in the passenger side and loosen what you need to get at the core and then go outside and with the pliers or screwdriver loosen the two hoses going into the firewall, they are both together, one on top of the other , then replace. If not pay from $30 to $60 to get it at a mechanics shop. Any other major problems, I hear you have to promise your first born. Labor is high.

Answer 2

Well, if you are seeking least expensive way, call local " Auto Wrecking" for availability and cost. Or, you can call local Dealer Parts and get ready for the impact, but, will get original equipment. Or, spending a little time on phone talking to Auto Parts Stores for price/availability. Keep all this data on a sheet of paper so you can review what has the better part for the least price. A friend, or friend of a friend can do work reasonably, cheap scares me, reasonable better !! Good Luck and God Bless !!