Cost me around $20,000. I did mine full-time and it took me 4 semesters to earn it. I think part time MBAs usually need about 2-3 years.
JSPilot; If you're looking to fly the line the next 30 years then it probably would not be worth it unless you plan on starting a business on the side. Then it might be justifiable.
RRambone; you are correct about the Aviation MBA. The core courses are the same as a regular MBA. You take an economics class however the focus of discussion, reading, case studies, and assignments center around aviation. Same with Finance, Accounting, labour relations etc...
Both a good and bad thing. GOOD if you KNOW you're going to pursue an aviation career and have a real interest in aviation business. Also GOOD for building contacts within the biz. I've got friends and former classmates spread out in basically every airline head office in the USA. That could come in handy someday, who knows.
BAD because it could conceivably make you look a bit less marketable to a hiring manager outside of aviation vs. somebody from a more traditional MBA program.
Hope this helps.