Add eCommerce to a website

We have designed and are building a website for a new kind of customer survey tool. Instead of the conventional model that lacks a structure, our product allows a business to design a survey for their clients and feed back the responses into the business plan. A business gets the first 100 responses free and then the pricing model is simply about the number of responses the business wishes to buy. A business can get a “discounted account” if they are charitable, educational or medical. So, the pricing page asks for: number of responses required; whether it is a full or discounted account; whether they are to pay value-added-tax; what currency. Then the software uses a look-up table to decide the price to pay. We need the pricing page to be implemented as well as the eCommerce. We need to implement payment forms as well. In the prototype, these are implemented through StripeJS, but we are open to other merchant/payment schemes.