This topic has come up several times before, best bet is to search and see what was said
it boils down to if you want a stand alone program coded to your specs (expensive and time consuming), can get coded for much less over seas but run the risk of "dirty" code or no product made
leasing the program, and it is a plugin on your site.
just start goggling different companies, if memory serves there is one from Florida that get good reviews for leasing.
There will always be the argument of letting the customer design VS design as a service.
In the end there is no denying that Vista Print (or any like company) has the right idea you are able to make sales 24/7/365 with an online designer and you don't have to waste your time on the "simple" layout and can focus on the projects that do require the "professional" design