We bought a new plotter/GPS this winter, and while the provided mount would have 'worked', I wanted to be able to swivel the unit port and starboard depending on what side I was steering from, and that mount wouldn't accomodate that.
So I checked out various right-angle brackets available for BBQ mounts, down riggers etc and didn't find anything that would really work well and the prices were a bit much anyway for a compromise.
I knew I had some epoxy resin and cloth at home, so dug out an old shoebox, lined it with wax paper and layed up a bracket inside one end of the box. Added a gusset, glassed that in and then let it cure. Later trimmed it to fit the plotter bracket base, and mounted it all on the pedestal pod as you can see below... Total cost zero since I had the stuff 'left over'... but I suppose there's maybe $20 worth of resin and cloth in it.