I know of no such plugin. What about having them do the budget in a spreadsheet? You (the teacher) set up the spreadsheet with the budget categories and the formulas and make it available to them as a resource. They
download the spreadsheet during the quiz and enter their numbers. The only challenge is how do they submit the finished spreadsheet to you. Unfortunately, quiz questions do not allow attachments -- not even essay questions (vote for
MDL-8229).
So you are probably forced to convert this one question into an "
upload" assignment, which allows an attachment. You can have them do the assignment under test conditions. It's not ideal, but it's a workaround.