Actually, you should have named this 'how long can I survive on bootstrapping'. It seems as though your answer is 'not much longer' at your current trajectory.

So you need to change something.

It sounds like you couldn't afford to release a free version, with all the costs involved. So don't. Stop releasing the free version. Think of a price you would be comfortable charging for it.

Now double that price. Chances are you undervalued what people might be willing to pay for your application. You have a growing user base, but most unfortunately if it grows too much you'll just be out of business that much sooner.

Sure, it wouldn't hurt to keep talking about acquisition. The beauty of that is in most cases these talks take forever, so you have plenty of time, and can always back out or tell them you'd like a few more months. The downside to this is they might just wait until you run out of money, and then whatever small amount they were offering you will become surprisingly smaller. When they have a meeting about whether to acquire your product or not one of their strategies is going to be 'let's wait and see what happens in the next couple months'. It's only to their advantage.

And at least give us the link so we can let you know if we would pay for it! Your company is failing, this is not the time to be discreet.