need pricing for new software

[Sail]

I'm completing a plan for the development of new software that will be used by both, retailers and end-users/consumers. I'm not sure how and who should be charged although I've had experience sourcing software in a corporate environment. The application will be transactional based. For retailers (the business to business/B2B market) to buy into it, I don't think I'd initially charge (for a year or so) a licensing fee, but charge by transaction, soooo for everytime a consumer uses the app at the retailer, the retailer pays so many cents per product bought by the consumer that's joined the application's website. Then, there's the consumer who wants to track the details of the his/her purchases using a few of the app tools. I've already determined there's a consumer demand for this. I can also charge the consumer a price as well for usage. Thoughts on new software pricing for the retailer and the consumer is appreciated.