Here’s what you need to do to start facemask therapy in a growing patient with a retrognathic maxilla:
(note links are just suggested- you can buy from any vendor):

Buy it from ebay (or any ortho company)
Also need extra oral elastics: or
I usually do 8oz 1/2 inch but some people do 16 oz but you can always work up to that if you aren’t seeing results.
So around $50 ish  and the elastics can last for many patients.