Man up and pass on the cost. In some sense in this situation you are a slave to market forces beyond your control. Price gouging once they've built lock in on an API is pretty much a natural part of any service's lifecycle. If you can afford to ride it out, eventually the forces of competition will take over and prices will come down a bit.

From the way you talk about potential partnerships or help with gmaps it seems you really believe in the value of your business. That's an asset. Try to articulate this value more clearly but understand that gmaps is unlikely to just "help you out" or "invest" in you at this stage since: 1) it's not their mandate and 2) they're the incumbent and potentially you are eating a piece of something google wants to do.

At the stage you're at ... 4-5K MRR 25-100K DAU ( I'm guesssing ), and suddenly a slave to a price gouge, an investor can help you out. Definitely try to find one. There's probably a lot for them to like in your situation, not the least part of it being that you're to some extent desperate for their help right now.

I love your non-defeatist attitude. Don't give up. Keep going. You know what you're doing is somehow close to how Airbnb started right?