Idea Could Use Some Feedback

[mtheory]

We recently started a niche social network and have been thinking about ways of building members. We've hit the usual suspects like MySpace to reach members of our target audience but we now have funding available to take it to the next level.

Starting an affiliate program comes to mind but I've seen many other membership based sites waste a lot of money for low quality(untargeted) members that don't revisit or use the site.

My idea is a contest that would give away cash and prizes. The angle I think might work willl be to offer an initial first prize of $500 after the membership drive and add to the prizes as membership builds, based on the increase in members.

For example:

During the membership drive period we would add $100 to the grand prize and create a runner up prize of $150 for every 1000 member increase at the site.

So if we were to gain 25,000 during the drive the grand prize would then be $3000 with 25 additional prizes of $150 available.

Works out to be .27/member aquired.

Any thoughts?