I made my own using the voile kit and an old board that was collecting dust. You don't have to get split specific bindings either as the kit come with a plate which will accept a normal pair, however it does raise the bindings up slightly so you aren't right onto of the deck anymore.
It's actually quite simple to do, the hardest part I found (other than sawing a perfectly good board in half) was deciding on stance and angles as those are basically fixed.
I used it for both avy courses and a pretty light touring season before commiting to a production split board and had no complaints on ride quality etc. I can't say it came out perfect but my take is that it was a pretty fun project to build it up and dip my toes into touring before investing in split specific gear, so if you can't find anything second-hand you like and you've got a board to use then why not?