It would be €529 /month for 20 users but wouldn't they need to possibly support way more users than that? I wish we had a client-side solution that could infinitely scale beyond having users run their own node.js proxy.
And also for this specific need case (just proxying and embedding) the 'spark' plan at €19 will be enough though. Also for these non-for-profit usecases I'm happy to sponsor access.