I built my own out of 2x4 tube. With about $130 worth of steel and $350 for a front crossmember, I had what I needed to make a frame. That was 2 years ago

I know steel is much higher now, but the price of pre-fab frames is much higher as well.

I was going to buy one from Fat Man Fab. before I decided to make my own. They seemed to be the best value at the time.