I'm by no means the expert on these boards, but I would say if all you are wanting to do is collect the figures that came out from the new line, then you should be pretty safe. finding a complete he-Man, Skeletor, Man-at-Arms, etc from the classic line shouldn't be too hard, or expensive really. There are a lot of people here on the boards that would probably have them or there is always ebay. Realistically it's the later released or accessory heavy figures that are hard to find complete, and therefore pricy (like a 100% Orko for example). i'd say a fair average price for a complete vintage (general) figure with a shipping cost factored in should be in the neighborhood of $7 to $10 US dollars.
I hope that helps!