Years ago you could find several good used regulators on Ebay that were very low priced. I just found this one, https://www.ebay.com/itm/Concoa-Prec...MAAOSw7dFeww05
which is good, but not cheap. Then I found https://www.ebay.com/itm/Used-Linde-...gAAOSwkaNeMxkP
which is much lower priced, but appears to be a two stage regulator - good. So, I suggest you keep an eye on Ebay in hopes of finding one that is a good buy and well adapted for the pressure range you will want.