Signal is one of the most important anticapitalist tools we have right now. It's FLOSS, free to use, privacy-preserving, and run by a (real - looking at you Mozilla) nonprofit. But that doesn't reduce the bills Signal has to pay to make the service work: https://signal.org/blog/signal-is-expensive/
I know several people here have issues with Signal's centralized nature, but it's the gold standard in encrypted messaging for a reason. Go donate if you can - we all deserve privacy.