1GB actually at that tier. Kuma uses like 200MB idle with 80 monitors. You'll be fine.
What do you use for monitoring 50+ client sites cheaply?
In France we have StatusCake, they have EU servers. But their SMS is expensive too, same problem. Self-hosting is the only sane way for 50+.
StatusCake's good but expensive. I've got Uptime Kuma on an OVHcloud Gravelines VPS, 3 euros. SMS via Free Mobile API, free if you're with them.
Free Mobile API... I am in Brazil, not France. Lucky you!
In Ukraine we use BotFather Telegram bots for everything. SMS is dead technology, expensive, unreliable. Convince your client, beto60. Or charge them extra for SMS specifically.
Charge extra... this is good idea actually. Client wants SMS, client pays SMS. Not me.
If the client insists on SMS, look at AWS SNS. They accept international cards, pricing is per-message not monthly. For one ecommerce site it's cents, not dollars.
AWS SNS + Uptime Kuma webhook. Done this combo. SNS is reliable, prices are on their site, no surprises.
AWS... I am scared of AWS. Always hear stories of bill surprise. But per-message sounds safe. I will look.
AWS billing horror stories are from people leaving EC2 instances running. SNS is different, you can set cloudwatch billing alarms. Very hard to spend $79 there.