and just to add some more to what @maple said here https://computerfairi.es/@maple/100238728808816998

- hetzner.cloud runs mastodon for 6€/month
- scaleway.com for 8€/month (but you need very reliable backups)
- instead of Amazon S3, wasabi.com is 5$/month up to 1TB
- you could also host both on a smol dedicated server with a disk, it's not very fast but would prolly handle it fine for 15€/month https://www.online.net/en/server-dedicated/start-2-s-sata

(and the hardest part is taking care of it afterwards and keep that in mind)