I was in the exact same position as you, looking at paying over $100/mo for a simple side project on Heroku. I wound up deploying it to my own VPS for $5-10/mo instead, and it actually ran faster was was much more reliable.

I am working on turning this into an app that others can use too. It's still a ways away from real production use, but I am close to a closed beta. If you're interested, check it out:

https://www.seamless.cloud/