POS terminal idea

I have been discussing with a friend his new business venture. The concept is simple. Retailers offer discounts to card-holding customers, customers pay an annual fee for their card. The business model appears ok to me, but there is one huge gap in it. As things stand, they will have no idea, nor will customers or retailers have an idea of how much customers have saved / related turnover. When it comes to renewal time after a year, I suspect a lot of customers will not renew because of that. My suggestion to him, subject to cost (which I hope someone will provide estimates of), would be along the lines of: At each retail outlet have a card reader (a bit like the small ones used for credit card transactions or even the very small ones used for online banking), insert the card, the standard price & the discount. Obviously quite a bit of code is needed to do all of this, but it would enable that business to provide retailers with the turnover from these customers, and customers with details of what they have actually saved when it comes to renewal time. The job would involve all of the coding, sourcing the necessary machines / card producer etc. This is a very open spec I know, but if somebody knows enough about what is involved it could be implemented quite quickly. Any thoughts appreciated. I have no idea what skills are required.