There are agencies/dev shops that -- assuming they like your idea -- will take a piece of equity and charge a bit less.

Go with one of these shops so incentives are aligned and they truly care about building your product rather than just billing hours. I know (but don't work for) a couple and am happy to provide a referral, feel free to send me an email.

As for cost, I find Gigster's pricing examples to be pretty accurate: https://gigster.com/pricing