You might have already thought of the following, but here is a couple of ways:

1. Offer a lite version which is free, and try marketing that and leveraging on those users to upgrade to a paid app

2. Approach iPhone app review sites and pitch the app to them for a review. (you might also consider advertising in these app review sites to begin with and to gauge the initial response)

I agree with you that blowing away your hard earned money on a big marketing spree might not be a wise decision. So, starting off with a smaller site and watching the initial reactions would give you more confidence on what to do next.

All the best :)