"LOADED" 10 inch trailer brake backing plates for your application are cheap at $29.00 each. This includes the backing plates, brakes, electric magnets all in one package assembled and ready to install. Add the new complete brake drums, seals and bearings you will need at about $50.00 each complete and you now have the brake parts to complete your trailer brake upgrade on the trailer. Basically for about $200.00 including shipping from Etrailer.com for the trailer brake parts you can convert your trailer to 10 inch electric trailer brakes on a single axle 3500 pound or less GVW trailer.
These parts are an EASY BOLT ON to your trailer. 4 bolts to attach the backing plates to the mounting plate you confirmed was already on your axle and the easy replacement of the current bearing hub on your trailer with your new brake drums and the dirty work is DONE!
The wiring of your new electric trailer brake setup on the trailer is equally as simple.
One wire from each of the backing plates run to ground and the other wire to which you add wire runs to the front of the trailer and into the proper location on the 7 pin RV plug you will now install on your trailer replacing the flat 4 pin plug or 6 pin plug that is probably on your trailer now as you will now have a minimum of 5 wires active on your trailer plug and maybe more if you are powering/charging a battery
from the tow vehicle. You can run an individual wire from each backing plate to the same pin on the trailer plug or run one wire that both trailer brake backing plate power wires attach to back near the axle and run one to the front of the trailer plug.
You now must purchase a electronic brake controller to make those electric brakes you just installed work. $50.00 or less for a basic brake controller. No need to get fancy here we are not stopping 10K pounds. More like 3K pounds or less.
Again an easy install. Find a good location to mount your brake controller that you (The Driver) can access the brake controller in the event of an emergency if you need to activate the trailer brakes alone/separately to control trailer sway or some other issue. Take the wires from the brake controller and connect One wire to ground, one wire to power, one wire to the brake pedal switch and run one wire to the rear of the tow vehicle trailer plug in the proper location. With a little luck your tow vehicle is already factory trailer wired and the installation of an electronic trailer brake may be as easy as plug and play.
Go out for a drive to adjust the trailer brake gain on the controller per the instructions included with the brake controller and you now have trailer brakes.
Hardly a $1000.00 job.
$500.00 or LESS including the PARTS & LABOR if you don't want to do it yourself. This is a $250.00 job for parts if you do the work yourself for the trailer you described in your original post.
IF your state requires a "Trailer Breakaway System" on your trailer now that you have electric brakes add another $50.00 and again an easy to wire system when you make the trailer brake system upgrade.
A point of note:
I would install 10 inch brakes on your trailer and NOT 7 inch brakes that are typical on these trailers if you are adding brakes. The 7 inch brakes are small and provide very little electric trailer braking. 10 inch electric trailer brakes make a WORLD OF DIFFERENCE when stopping your tow vehicle and trailer. Yes if you have to change wheels/tires to make the 10 inch brakes fit I would do that without question. Do it right once and be done with it!
Here are pictures of how the 7 pin plug must be wired: