Currently there's only one organization manufacturing them — Marcodi Musical Products, run by Tim Meeks and Jason Melani out of Glen Arm, MD. Tim Meeks was the original inventor and developer of the harpejji, and Jason Melani heads up marketing.
Their cheapest model goes for $3200, has 12 strings and a 3 octave range. The larger base-model instruments go up to $6400, and the company offers high-end customization as well.
independently-produced articles about Tim Meeks and his harpejjis — 
Tim Meeks owns several patents relevant to the harpejji, so it may be 20 years before we see the instrument manufactured by other people. However, it may appear on the used market from time to time, so that could be a less-expensive option.