Signal had 40 million active users in 2021 [1]. With 14 million in infra cost, that comes to .35 per user/year. Total expenses are about 33 million, so about .825 per user/year. All in all that seems very reasonable.
I'd be happy to pay $1/year for signal, and I'd pay $2/year if it were decoupled from my phone number.
I'd pay substantially more for Signal if I could bot accounts.
I'd like a signal daemon on all my servers for alerting which could message me via Signal. This is worth a monthly fee to me.
I know people running small businesses who would really like to have a business Signal account: an ability to send Signal messages as a business identity without tying it to some specific phone number. This would be worth a subscription even if they had to get their customers to install Signal.
Signal need to figure out what product they sell that's going to fund the privacy objective: because there's plenty and they're worth having.
If you want one for just personal use; this works well: https://github.com/AsamK/signal-cli
Just sign up with a Twilio number (using voice call) and you can make your own bot.