Ask HN: Opportunity to earn a cut on every transaction. How big should my cut be?
Yesterday, I presented a "no strings attached" time and cost estimation for developing the initial version of the app. I took into account that the estimated cost might not fall into their budget and presented two alternatives. Their business model is primarily a transaction based one and is very sound. They have sole rights to distributing the virtual product/service and key retail vendors have come on board with letters of intent. As I suspected, the quote did fall out of their budget range and at that moment I decided to bring forward the alternative somewhat "informal" proposals.
Option B. My business owns the IP on the software. They use it and pay just for maintenance costs.
Option C. They pay less for the system and I get a piece of every transaction.
Today I found out that they really liked the Option C. Now that the two alternative proposals where informal, they want to see something on paper and then we can come back to the table thereafter.
As per Option C, what do you fellow hackers think would be a good deal? What would be a realistic percentage, per transaction, to ask for? (Taking into account that their business very strongly depends on the system I will build and maintain. Also I was very highly recommend for the job by one of their current business partners. :)) Also, how much less should I charge for building the system in relation to taking a cut in the transaction costs? (Is there maybe a ratio as a rule of thumb?)
Any suggestions greatly appreciated.