Would you be willing to share approximately what it costs you? I saw your post here and deleted-before-posting speculation that Patreon simply can't make the numbers sensibly work out (bearing in mind they have to grow by offering an attractive package to both those who donate and create; if, for instance, 50% of the "donations" go into tax compliance there simply won't be any donations anyhow), but if we can get real numbers that would be even better.

Of course, that's assuming you have a similar problem to Patreon, where the author claims that every patron would be involved in the VATMOSS transaction, which I can't speak to at all. If it's just a line-item per book for you but a line item per EU patron for Patreon that's not comparable.