How should I go about finding and hiring a developer for an app that I'm building?

I have worked with some success on upwork.com.

I would suggest to lower the budget but pay them in time right after they send you the project and you have properly tested it.

If you want to go cheap, you can outsource and deal with the potentially lower quality. You can bring on co-founders and give up part of your company (don't take this lightly but can be very effective for the right partners). If you can at least put down a decent down payment you can still go with a dev shop assuming they are ok with waiting for full payment after an agreed upon amount of time (this isn't impossible, but not all dev shops will be open to it).

In general, you get what you pay for. Really no getting around that. We can chat more about it on a call if you want.

Hello.
You can always turn to UpWork, the biggest workplace for developers. It's easy and you will find exactly who you are looking for. Or turn to MobiDev (https://mobidev.biz), it'll be faster and more reliable.
Good luck!