I will also add, that no matter how I try, (and I've built 4 different sled/bike trailers) in the last 4 years. NOT once was I able to complete one for under $600. Axle $125, wheels and tires $150, metal $150, hitch parts, wiring, 3 sheets of plywood $120, bearing buddies, lights, paint, etc.
The real advantage is that you can custom build it to a particular vehicle or size or application, including color.
I bought a 24' Classic dominator, we were going to a race with a trailer to start with, to pick up the new trailer... How was I gonna get 2 trailers home? We read up on the new trailer and built a flatbed trailer that fit inside the new enclosed trailer. So that was a good example of how I was able to build a specific trailer for a specific need. Couldn't buy one that size, 84" wide, not 96.
If your time is worth anything to you, finding a good trailer in the $400-$500 range is a bargain. You can still trick it out.