Does anyone know of a good conversion tool to convert transportation related EDI formatted files to CSV format?

I think you are going to find that your EDI data is hierarchical and cannot be converted to a flat CSV file unless you are interested in one small subset of data. Since your client is undoubtedly already using EDI data in their workflow they may have a requirement or expectation of what data they want to manipulate in QuickBase. Perhaps this understanding of the desired QuickBase schema will help you understand the mapping between the EDI files and QuickBase table/fields.

This website has information on conversion tools involving EDI data:

http://www.xtranslator.com/index.html