I'm wondering if anyone here uses some kind of shop systems ("Web-To-Print") for selling their prints?

After googling around a little bit it seems that there are some really expensive complete systems, like EFI Digital Storefront, and many (also non-free) Magento customizations and plugins out there.

Personally, I really like EFI's solution because it nicely integrates with their Fiery product line, but it lacks some important features like automatic page size detection for LFP products and Paypal payment.