How much is TAC sensor in 2002 Chevrolet Trailblazer?

I have a 2002 Trailblazer and took it to Auto Zone to have them check the codes for the service engine light being on. It came up with a P1512 and P1516. Those both have something to do with the throttle actuator. I'm not sure what this means. Could someone give me an idea of the amount of work and cost that will go into this? Thanks.