It depends a lot on your time and experience... Also, what you want to know. There's no guarantees at all with a SaaS startup, and if you can increase your knowledge base at a minimal time sink it may be worth it. I have a dozen things I tinker with and no expectations, so I treat it more as a hobby.
I am spending about $140/mo on a dedicated server currently, mostly because I want to run my own mail server without depending on a relay host or nickel and dime costs ($2-10/mo per address). This now runs just about everything I use. Nearly all my apps are dockerized so I can port them to another host pretty easily.
I've also been playing with writing for Cloudflare directly (workers & pages) as well as CockroachLabs (CockroachDB Cloud). Both with relatively low startup pricing and can grow as needed based on usage/demand, both with a relatively clean self-host strategy as an exit.
It would be too easy for me to wind up paying $20-30/month or more on a dozen or more projects. I try to keep this down, as if I don't touch something for a month, or don't complete it for a year, it adds up quick... If I keep baseline costs low, it's less of an issue.
If I was 20 years younger, I'd probably have gotten more of these things done or put more effort in. The tech costs are a lot better today than 25-30 years ago when I was starting out. But I'm still pretty mindful of it.