Going back a few years, but Sage also used to provide a read-write API (not ODBC based) for accessing the data in their products.
I'm not surprised that you need to join the developer program - Sage is a traditional closed source commercial application - it's unlikly to have open source options available for it.
Joining the dev program used to be free for Sage customers, which the people you are working for should be, surely...?
EDIT - yikes, not free any more
