@Jon, you are probably on target with $$.
Well Ian, maybe the community here will be able to help (for free.) Realize that Moodle is free, but that your school chose to pay for its LMS, D2L. So, since your school obviously has money, it should be willing to pay to have question banks converted.
As a suggestion, maybe a third-party quiz development tool, like Repondus or ExamView, might be able to read the Moodle question bank and then convert it to a format that is acceptable to D2L. I have an old copy of ExamView, which has come in handy at times to get questions into Moodle. I haven't tried to go the other way.