All depends on what country you are in and what Mac you are referring to. A good idea of the price for memory upgrades without getting ripped off is at Crucial. Use their memory finder on the front page to get the right Mac, then they tell you what type of memory and how much it takes and what you can buy as an upgrade.
Ah, forgot to mention its for a macbook pro.
Some of the linked ones say ECC and Heat Spreader. What are those, or do I want them even?
Also, If I have the Intel Core Duo 2.16 ghz is the max 2 or 3 gigs of ram? I have seen 2 different answers.