IE Business School in Madrid has an interesting offer for alumni of masters' graduates from the school and its sister law school. The "MBA Key" programme is a two months core course plus a semester long module based on the IE MBA's concentration. Completing both leads to an MBA from IE, for a greatly reduced cost of 18,000 euro.

You can read more at http://www.welcomeback.ie.edu/programs/mba-key

This is an interesting offer, since you could get an MSc in finance or law and an MBA from IE from slightly less than the school's full-time MBA.