Build an Online Store

We have a online store called [login to view URL] that we need some assistance on. Basically what stor is, is a platform whereby a user can buy, store and download digital gift or membership cards (retail vouchers) We will eventually have a list of all the popular retailers or clubs, whereby the end user can browse through, and once they have made a decision - they can purchase the voucher online. Now comes the tricky part, once the user has selected and paid for the voucher - we one one or two things to follow: 1. the digital card should be emailed (at a correct size) to the user for later use or whenever they want to use it. 2. it should be stored in the users account section, somewhere where the user will be able to login and browse through a list of there purchases. Maybe select one, they should have the option to then print it, re-email it or download it to their pc or phone. Please let me know what you can recommend and also what it will cost. We would like to start off slowly and then build the platform up as we go.