A float of around $1000 would probably be able to get the site started decently (for the provider offerwalls that pay on a net 30/60 basis), and then monthly server costs of about $200 as a decent server is needed from my experience once the user base gets active (when originally took 2 weeks, now would take probably 2 days of advertising with about $50 total cost of advertisements on various PTC websites)

PM me and I can give you my skype for any questions