That doesn't seem right. There are some 37,000 active Lemmy accounts within the past month.
https://lemmy.fediverse.observer/stats&months=6
It's well-known that lemmy.world is the biggest instance (or close to it). In addition, there are hundreds of thousands of Mastodon users, of which at least a good few per cent are mastodon.world users.
This would give the Fedihosting Foundation a user count on the order of 10^4^ users. And since their hosting cards are on the order of 10^3^ EUR, this would mean each user costs on the order of 10^-1^ EUR.
For comparison, Reddit reported 10^8^ daily active users. They also reported cost of revenue at 46 million USD per quarter, meaning they spent on the order of 10^7^ USD per month. So their cost per user is 10^7^ USD divided by 10^8^ users, or 10^-1^ USD.
This seems to show that Reddit and Lemmy cost on the same order of magnitude to operate (which, keep in mind, can still mean a 2x or 3x cost difference).