the best approach is to build a mockup that has the signup and intro pages, and a non-functional signup page(i.e. don't store credit cards)...then run $500 worth of adwords through the site and see if anyone bites.
if $500 is too much, stop thinking that. Building out the feature set to make the site functional would take you quite a bit of time...even if you only "charge' yourself the minimum wage, you'll still end up wasting more "money".