Go to the GM dealer and have them look up the disc brake bracket setup for a 99 and newer truck. I'm sure it'll be less than $100 a side. You can get the rest of the components at Rockauto or your FLAPS. You'll have to drill the rotor for 5 lug though.
I spec'd this kit for a 2500 series truck, it was only $60 a side. The shoe, hardware and backing plate was only like another 30-$40.
http://s1074.photobucket.com/user/wh...83557604518159