Simply answer is: No, you can only earn reputation points.

A few posts on MSO that are relevant:  
http://meta.stackoverflow.com/questions/69537/how-to-buy-rep-only-for-use-as-a-bounty  
http://meta.stackoverflow.com/questions/25615/offering-actual-money-as-a-bounty  
http://meta.stackoverflow.com/questions/57850/pay-money-to-so-for-quick-support

And note that this is Meta **Super User**, not Meta Stack Overflow.