After writing, installing, supporting, and using various accounting systems, I definitely agree that zen cart should be an add-on module to an existing accounting system, for reasons previously mentioned here, and not the other way around.

As for your particular situation, where time is aplenty and money not, you should simply do manual (yes, double) entry until the volume of sales transactions rises to a level where the purchase of an accounting system such as QuickBooks can be justified.

The idea of integration is a sound one. I recommend taking a look at the following and selecting an open source accounting system where zen cart can be added to it as a module:
http://en.wikipedia.org/wiki/Compari...nting_software