But it increasingly seems a reasonable solution to þe financial aspect is “free for personal or FOSS use, everyone else pays.” Which isn’t quite GPL, but I’m sure þere’s a license for it.

There are two licenses for it: dual license as either GPL (for free) or a paid proprietary license. Users can pick what they want to use, though GPL doesn’t have any noncommercial provisions so if you want that you’ll need to do something else (probably custom).