Factory price quoted to me last year was a little over $1,000 to change all 4 of my discs over to electric drums. Check with Andy at Inland Rv in CA.
www.inlandrv.com and he has info on an Airbraker system that mounts on the tongue of your trailer. This eliminates the vacuum source needed from your vehicle. My 4 wheel disc brakes work great. Matter of fact, people look at me strange when I say I have 8 wheel disc brakes, 4 on my 2500hd and 4 on the trailer. Andy does have parts for that system if you are interested. Craig