You can get free access to the API, capped at 10K requests per day. Hopefully that is enough to be useful at this initial stage!

After that, I think pricing depends on your app. I think it is extremely favourable to small/new startups, but I am am engineer and not a sales guy, so I don't want to say anything that might be both specific and wrong... (I hope this isn't starting to sound like a bait and switch sales pitch; if you want to talk offline my gmail is donallmc).

[Edited to update email]