Who's paying $70 on a regular basis?
It all depends on how long you think the member will stay active with that site (which is a crap shoot) You could send 1 sign up to a site that has a $5 trial & then recurs at $30 each month. If the sponsor pays $30/sign up, you get that right off the bat, regardless of if the surfer stays past the trail. But, say that surfer stays 2 months past the trial & you're on the recurring option - at 50% that's $32.50 for you. If they stay 4 months, that's $62.50.