>>mikece+(OP)
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.
>>V__+r8
Mastodon org + Mastodon.social also have costs of 0.6 EUR/year, though they have two orders of magnitude less users [1]. This is really what most social media costs. These rates are even payable by many in poorer countries.