I actually agree with you. However, the real reason is not the money. It is not being able to promote the product as an FDA approved product. They are done talking about the trials. They want to talk commercialization at the booth. Also, if they have a partner, the partner does all the promotions and marketing. so a booth would have been for both partner and MNKD.
The rented carpet space has already been paid. The physical booth is most likely rented and can cost $50k to rent, ship, set up, etc. The booth has been cancelled. Depending on the number of people attending, the T&E can be $100k. But I expect this cost to remain since the same people will be at the partner's booth.
Mannkind is at booth 1823 - 20x40 foot booth, which is pretty respectable size for this show. In perspective, Lifescan's booth is 30x50. Booth will be between AZ, Lilly and Merck. Proximity to a company is generally meaningless btw.
Not sure about current rates but sponsorship fees can run up to $50,000 a day. Exhibit booths are much less ($3250-$3450) but I am assuming they weren't planning on just a 10x10 table in the exhibit hall. So yeah, a table is a comparatively minor expense but not worth having someone manning it for 4-5 days and not being able to answer the inevitable questions that aren't allowed to be answered unless and until they get approval.