1) Work paid part time at something else.

2) Join an accelerator or similar.

Both have worked for me. There are other solutions too.

Also bank loan. But risk.

“Friends and family”/angel investors, too.

what if your project is a niche, you have no plan for an exit, how do you share profit with the accelerator?

Not all accelerators take equity. Some are pure grant funded such as one I used.