We use to build raised beds by hand, we always really liked them, except they are a hassle to build.
I got to looking up "bed shapers" and they look like a pretty easy concept.
I have 4 new hustler edgers, they are a 16" disk, they are a factory defect and are worthless as a edger, so I thought I would put them to good use.
I had the rest of the metal, so the only $$$ I have in this is just in bolts welding rod and time.
The main part of the frame that I used is 2 1/4" solid box, all the other metal I used is really heavy channel iron.
I am thinking about using all four disk, and then I am going to build a shaper box for the back of it.
Here is a link to the factory ones, mine isn't going to be as fancy looking, but as long as it can make a nice bed that's all that matters.