I haven't been to TSC to look but I can't imagine much for $100. When I redid my brakes on my 10,000 gvw trailer, the backing plates, shoes & magnet kit was about $70 for each corner. This did not include the drums that were another $40 or so. So, you have over $100 per wheel = $400. Now you need a wiring harness and plug, and all the labor. Better be a really cheap trailer.
Second, there is nothing wrong with a 2" ball.
Third, I would never tow a 7000 pound package without brakes. Remeber, I'm the guy who went over the cliff when my trailer was heavier than my tow rig's stopping ability.