Hello guys, I have a program idea and I want to start it out, so I want to ask if it will cost anything apart from my time to build and upload an app.

I know that I have to pay a one time fee to put apps in play store

No one can really tell you anything significant about cost until the person knows the idea.

Some programs require interaction with paid APIs. That's cost. You'll definitely have to host the backend business logic somewhere. That's cost. You'll definitely need the Internet while at it. That's cost. Etc. These are just technical expense sources.