Ask HN - Best way to run a promotional campaign for a startup?

I want to create a campaign where users would submit videos on "why they blog". It would be a 30s video MAX. The idea is to get them to sign up at our site which is blog focused. We would then take these video's and create a compilation video that will get our site's message across.

The winner would get an iPad or something similar (and yes we would actually give it to them, and we would chose the winner). Here are our main issues:

1) Nobody knows about us (yet) 2) Win an iPAD sounds kind of phony 3) I'm not sure what cost effective mediums we would use to get the contest going.

Obviously, we would post the contest on twitter, youtube and facebook.

Our budget is about 5-8k on this (including the purchase of the iPad). If I had 100k, I would put out ads on all of the major blogs and that would surely generate traffic.

I'm looking for feedback on what you think the best way to do this is, and the best way to reach the masses.