combining a flat-website with e-commerce!?

[dzdrazil]

My client provides a financial analysis/ statistical service and advertises primarily via their website.  However, their "website" is in reality about 6 to 8 flat files that she updates via her old Frontpage program.  She's so in love with the ease of Frontpage that she doesn't want anything more difficult than that to change the layout and look of things.

 

However-

-they want me to add a Flex program to display some of their data models, and for full access to it be sold (payments via paypal).  My initial hopes of using Drupal + the eCommerce module seem to be dashed, however, because they're skeptical of the learning curve and difficulty with maintaining a single web page via the CMS versus slopping some changes on Frontpage and re-uploading it.  They've even offered me a Frontpage license as if that would really help.

 

What recommendations do you all have for a Drupal-eCommerce-module like shopping cart packages that don't require a complete re-make of the way their business has run so far?  If they had a larger budget and weren't crunched for time, things would be easier for sure, but this is what we're stuck with.