I recently had my ABS module fail on my 03. I went to find a used one, they were between $250 and $300 used. Something like this is an unknown. As I understand it, especially the Kelsey Hayes units have problems. GM and Dodge use Kelsey. The PDC , Power Distribution Units, (Fuse box) has failures too. You can repair them yourselves if you have the right tools. Even I wouldn't mess with the ABS module. Having a RWD, my module is rare. The ones quoted to me were 4 X 4. Typically it's solder joints or PCB traces that fail.
I spoke with a friend of mine who knows these brake systems, as he was one of the engineers who designed them. Kurt at Shibby Engineering. He sent me to a company called Module Master. www.modulemaster.com The final cost with overnight return shipping was $163.00. They also give you a 5 year warranty. Pretty significant savings.
They are very responsive and from what i can tell, have a great reputation. The good thing about sending your module to them is they can find other things that may fail. They repair more things like your Dash clusters and ECM's. You'll have to look at their site for details. Too much to list.
I thought I would share this source with you. It looks like this is a better way to go other than used.
BTW, you can drive the truck with the ABS module removed, but you lose the speedo and lock-up on the converters. While Momma's car sits on a frame machine, I have to use ol' reliable.