Yeah I occasionally run into this. What I do right now is set up a one-off Typeform for that one payment. It's usually for $xxx or $x,xxx payments so it's worth, but not ideal.

I considered building a solution myself (quick way to receive arbitrary amounts through Stripe), but haven't come around to it yet.

If you build something that's simple and low cost (fixed monthly/annual fee) I'd consider using it.