If you are flying to or from Europe or the United States, to Asia or Africa and passing through UAE airports, you can obtain a special 96-hour transit visa. You must be sponsored by an airline operating in the UAE and you must have a valid ticket for your onward flight. Your travel documents will be stamped with an entry seal and there is no charge for this visa.
http://www.emirates.com/uae/TravellerInformation/before_fly/visas/VisaServices/96hrvisa.asp
USD 50
2) 96 hour visa pre-arranged:
http://www.emirates.com/uae/TravellerInformation/before_fly/visas/VisaServices/96hrvisaPre.asp
USD 20
但是UAE的政府网站上又说no charge:
If you are flying to or from Europe or the United States, to Asia or Africa and passing through UAE airports, you can obtain a special 96-hour transit visa. You must be sponsored by an airline operating in the UAE and you must have a valid ticket for your onward flight. Your travel documents will be stamped with an entry seal and there is no charge for this visa.