I know I'm late to the game here, but I would also suggest making sure you use SAW (surface accoustic wave). It uses a very durable glass touchscreen. Resistive is less durable, capacative is too expensive. Elo has a new tech (I can't remember the name of if, but it is really cool) that is probably the best possible option, but be prepared to pay for it.
Overall, the SAW screens like the 1545 Elo models are your best bang for the buck that you'll find on ebay. Personally, I wouldn't pay more than $100 shipped unless you absolutely can't wait. They regularly come up there for that price (15" models).