Looking for a leather OWB holster for a USP 45 on a budget.

I'd get a Bianchi 7 Shadow II pancake style OWB holster for that H&K USP 45. There are cheaper holsters on the market but few better than the Shadow II.

I have a Don Hume H710 belt holster for my Sig P365. It was about $35. I bought it thinking it would do until I got something better. After using it nearly every day for a year I can say it is an excellent product comparable to holsters I have that cost five times more.

Look into the 1791 holster line. They might have what you are looking for.
I bought one for my GP-100. It's a nice chunk of leather.

1791 or Azula. Surprising quality, affordable price

Make sure to check eBay, I’ve gotten some nice holsters from respected makers for pretty good prices.

I just found this one for mine.$27

https://www.holsterama.com/leather-dual-use-concealment-holster/