a little more info plese!!
original? never been touched? by looking at your year, i am gonna guess original.. miles on them?
take truck to a repectable shop and either have them physically check rotor for life left or guess. that will give you an idea of $$. my factories toast at around 36k. the ones on it now have ~39k on them and are in good shape - pads too.
look up one of our sponsors - frozenrotors- they are pretty good at getting back to you. towing your trailers - using the cryo stuff - may net you a little longer on the life of your brakes