The proper TPMS sensors that are actually going to work in your truck are going to cost you at least $42 each. That was the best pricing I found for them. You can get some different ones on eBay but I've heard of people having problems with them not working.
I'm not sure where you can get them locally. The dealership probably but you'll be paying more money. I got mine through Bully's Performance when I ordered my wheels and tires. You could contact either Andrew or Jeremiah and they'll hook you up. Be sure to mention that you're a forum member for the discount.