[jdmichal]

Why not give it the "Magic" treatment? Provider broadcasts emails / text messages. You can respond with some simple code, like "YES" or "BUY". Provider will then attempt to purchase at that rate using stored information. I would think the service fee would be best as a percentage with a minimum.

[rubyrescue]

That's tough because purchasing is often difficult. It took me dozens of tries to get a flight booked to Cypress once, through 4 cities. I ended up deciding the onerous itinerary was not worth the nearly free ticket. That's common so you don't necessarily want to insert yourself into these transactions for people, it really wouldn't scale.

[zacharycohn]

It's not just that it wouldn't scale - it wouldn't work even if I only had a dozen subscribers!