Originally Posted by David - PG

The more joins you buy that way the more expensive they will get because you will have to get less and less targeted traffic in order to scale up your numbers.

If you could "buy" the first 100 joins/day for $20 because you found a way to target your audience well. Things become harder and harder from there. Possibly it will cost $60 a join to go from signup #500 to 750 since buyers will become more and more scarce for your product. I would think this is a non-linear relationship, maybe comparable to bid/ask prices in spot markets.

Generating your own traffic is not a bad idea per se, you just can't economically scale it up indefinitely.