Yes, you can get both, although I would fail to see the point of why. If you REALLY enjoy econ, then get the MS. However, be sure you REALLY enjoy it. Once you get past the basic micro and macro classes, it becomes quite esoteric. Getting an MBA will get you exposure to those two basic principles of economics, which IMO, is good enough (but then again, I'm not an econ freak). Also, I think an MBA is a much more well rounded degree with exposure to a lot of general business practicies (accounting, leadership, etc), sorta the jack of all trades, master of none theory.
In the end it depends on what you want to do with your degree. To me, it seems like a lot of time to get 2 masters degrees when IMO, it would be better to get the Masters in one, and then if you really wanted to get antoher advanced degree, move it to a PhD. Same amount of time, but a PhD instead.
Disclaimer:
<----- Finishing MBA in April '06 (2 more semesters!)