4 Year old 1510 is probably work around $250 a terminal.
On the service frustration: As a former reseller I urged all of my new customers to sign-up for the 5 year cradle-to-grave service offer through Radiant. If something broke, it was simply replaced by a reconditioned unit the next day directly from the factory. It allows you to control you service cost by planning ahead.
There were early issues with the 1510 Power Supply that were resolved and most power supplies were replaced as a swap in the field. However, after that, the 1510 proved to be a reliable piece of hardware.
Service is expensive when you do not have a contract as Radiant charges a flat factory fee to service a unit regardless of what is wrong. If you are working through a reseller they add on their cost to handle the repair and reinstallation so it does get expensive.