They range from home made to aircraft quality aluminum. I used my Original Inspira frame with my Janome 6260 (6 1/2" throat) until I got my bigger machine. The only problem with using a roller system with a regular machine is that you are limited to about 3" of quilting space once you get near the end of the quilt. That's why I went with a bigger machine. I found I could do nicer designs with my DSM just on my table. That way I could do any size design I wanted.
But you might want to check out these sites.
http://www.flynnquilt.com/multiframe/description/
http://www.newjoyquilting.com/gold_standard.html
http://buildaquiltingframe.weebly.com/