For example, I could get a digitalocean vm with 2gb ram, 1vcpu, 50gb storage, 2tb bandwidth for $12/mo.
For the same specs at fly.io, it'd be ~$22/mo not including any bandwidth. It could be less if it scales to zero/auto stops.
I recently tried experimenting with two different projects at fly. One was an attic server to cache packages for NixOS. Only used by me and my own vms. Even with auto scaling to zero, I think it was still around $15-20/mo.
The other was a fly gpu machine with Ollama on it. The cold start time + downloading a model each time was kind of painful, so I opted for just adding a 100gb volume. I don't actually remember what I was paying for that, but probably another 20/mo? I used it heavily for a few days to play around and then not so much later. I do remember doing the math and thinking it wouldn't be sustainable if I wanted to use it for stuff like home-assistant voice assistant or going through pdfs/etc with paperless.
On their own, neither of these are super expensive. But if I want to run multiple home services, the cost is just going to skyrocket with every new app I run. If I can rent a decent dedicated server for $100-$200/mo, then I at least don't have to worry about the cost increasing on me if a machine never scales to zero due to a healthcheck I forgot about or something like that.
Sorry if it's a bit rambly, happy to answer questions!