I have no idea what such a collection would be worth, but the next best thing would be to figure out the least amount you'd accept for them and set that as a reserve price. If you sell them on eBay the theory is that the market will arrive at the correct price for you, because the second most eager buyer in the market will force the first most eager to beat his bid.

From time to time, reality does what the theory says it should do. Theoretically, at least.