When I was setting up one of these $5 per month services(a simple php Web shop, with shopware if I remember correctly) I tested it with 10 concurrent users (5 req/s or so on average) and the $5.5 per month instance handled it just fine.
Yes, the instance had docker and was in an auto scaling group to be rebuilt if anything fails. There were 3 containers running with strict mem/cpu limits. Nginx reverse proxy (all in 128mb of ram), a mariadb sql server with a minimum of ~300mb of ram and up to 512mb if available and the php/Web host with 512mb ram reserved.
Mariadb was tuned and shopware was tweaked, but that's about it. Everything run fine on a 2 core, 1gb ram instance. (has, not "has been" because a year later the shop closed for other reasons). So the morale of this story is, sometimes a $5 vps or an instance is the correct answer.
Yes, the instance had docker and was in an auto scaling group to be rebuilt if anything fails. There were 3 containers running with strict mem/cpu limits. Nginx reverse proxy (all in 128mb of ram), a mariadb sql server with a minimum of ~300mb of ram and up to 512mb if available and the php/Web host with 512mb ram reserved. Mariadb was tuned and shopware was tweaked, but that's about it. Everything run fine on a 2 core, 1gb ram instance. (has, not "has been" because a year later the shop closed for other reasons). So the morale of this story is, sometimes a $5 vps or an instance is the correct answer.