How Do I Market an iOS app bootstrapping and without being obnoxious?

I, and a team of developers, have recently developed a free iOS app called Vinny. I've been reading a lot of app post-mortem stories and where most developers go wrong is with marketing (or lack thereof). Of course after all our hard work, we don't want to fail. We've come up with a few ways to get marketing done but because of the digital age's saturation, a lot of marketing channels have put up tape that keeps us from really pushing hard on our app unless we have money...which we dont.

Anyways, I thought I'd sign up for a tech forum to see what people would have to say about the issue and if any of you guys have suggestions or ideas for me.

Oh, also, Vinny is a VIN scanner that reveals the dealer's cost on used cars based on auction transactions.

Thanks in advance.