Well, you said you'd be going the eBay route, and the prices are VERY reasonable.
My 12" iBook is one "sub-generation" behind the current ones (it has a 1.2 GHz G4 as opposed to 1.33 GHz and does not have blue-tooth) and I paid a modest $650 plus $30 for shipping.
Now, as far as why apple products cost more than competiting products brand new-
This has to do with Apple's very different business philosophy. The reason your Dell computer costs less than an Apple is because Dell (along with just about every other consumer electronics company) is willing to make sacrafices to get the product to a certain price. For example, if they want the product to cost $1000 but at a given point in production it is looking more like $1300, they will do things such as use a lower-quality LCD panel, use cheaper internal components, etc. to shed the price a bit. Apple, however, first selects what they want the product to be, uses good (not necessarily the best, i'm sure there is a better 12" LCD panel out there than the one in my iBook) components, and THEN tells the consumer how much it is going to cost them.
Please remember, I am NOT an apple fanboy or anything like that. This is a conclusion based on doing legitimate research (which stemmed from curiousity) about Apple and their business practices.