Have you considered self-hosting a payment page? I'm asking because I've been building Open Payment Host[1] a self-hosted FOSS payments host supporting multiple payment gateways; still very much a WIP but I hope soon it will be viable enough for someone like you.
P.S. Please ignore the AI autocomplete feature, I included it as part of Google hackathon to raise funds for the project; I'll be removing it in the upcoming release.