Thats not going to go cheap. I got mine from ulnadoc (site member) at a good price, but he was getting rid of an extra.
hopefully you find your “ulnadoc” and get one at a decent price.
Its a useful attachement, but very limited on how much you can do with it. It might be worth your while to look around for a used mill. Even a bench top one would be good. Might cost a little more, but you’ll get much more capacity.