If you are interested in staying with toyota stuff i used this on my rig and it has worked out great....
http://www.pirate4x4.com/forum/toyota-truck-4runner/1034855-new-disk-brake-conversion-kit.html
depending on how you get the parts it can be more or less expensive ....i chose to get the caliper brackets and bolts from them and source my calipers and rotors locally, and if you get the calipers from a junk yard it could be even cheaper.
i wanted to stay with Toyota stuff, I liked the whole idea of having a slip-on rotor and the ability to have a spare axle shaft with nothing else special that you had to have (such as a spacer plate like some of the other kits have), that way in the event that you break a shaft all you have to do is take the caliper off, the rotor off and slide the new shaft in...
when doing this conversion you will have to:
remove the drum from the assembly, the shoes and any other hardware on the backing plate
Cut the backing plate around the axle tube mounting flange, CUT on the backing plate (this will look like a square around where the axle studs bolt to the axle housing)
After the backing plate is cut away there will be a piece of the plate left between the bearing pocket...you will have to knock the studs out of the bearing pocket to get what is left of the backing plate away from the assembly, after it was free from the bearing pocket... just cut it on both sides of the square to be removed (this piece of plate can't be remove unless cut, because it can't slip over the bearing pocket or the end of the axle shaft)
Reassemble the studs back into the bearing pocket (they are splined)
Clean it and that is it.
install the shaft back into the housing.
bolt the brackets on the axle flange.
slip the rotor on.
bolt up the caliper.
it is a simple setup
Hope this helps.