I just convered my Trail Rite trailer from drum brakes to Tie Down stainless steel disc brakes. Try
www.championtrailers.com.
http://www.championtrailers.com/TIED...BRAKE_KITS.HTM
For a single axle, it costs around $465 with shipping for the single axle kit which included a new hydraulic actuator, new stainless steel lines, reversing soleniod valve & shipping.
I have never replaced brakes, packed bearings, etc, but I was able to do all of the upgrades myself. I spread it out over a couple of evenings and finished it over the holiday break.
When you call Champion Trailers make sure you tell them you have a Trail-Rite trailer because the seal sizes are not standard and they have to change them out.
Good luck... you can email me with questions.