I don't have an answer to contribute, but it made me think about several situations in our lives regarding paying:
When after two years of it being just David, Red, and me in a romantic/sexual relationship, and I wanted David to play as well, we "dated" my single female friends and acquaintances to see if they were open to playing with hubby. We paid for everything (including separate rooms on vacations) and expected nothing. It felt right and worked out well whether something happened or not.
When we became a poly family, we set up a strict system where we all contribute to an account for household expenses including the children regardless of parentage. Clair gets one-fifth of our income for being the stay-at-home mom. It's worked out well.
We now regularly play with Shannon and Joe. Whoever travels pays their own airfare. Since they don't have kids, we stay with them. If they visit us, they stay in a hotel and pay for it. They are eager to see us and it's worked out well. They do let us pay for dinners and other things.