RMB 5600 is hilarious. For that price, you should be getting a stretch limo with full champagne service, flag flying on the front, girls....well, never mind.

Looking at my trusty handy Beijing City Weekend magazine, you might try the following for a per-day rental with English speaking driver (I have not used so cannot give first-hand report):

Beijing Top-a-Car Service (scroll to "Daily Car Service" where they have a Simitai trip listed with Audi A6 for RMB 1500, Benz S350 for 2800. (http://www.expatslife.com/htdocs/epages.asp?id=24

Beijing First Choice Car Rental Service (pricing structure a little different so make sure all-in costs are calculated/estimated upfront for you. Looks like it will work out about the same as Top-a-Car)
http://www.fccars.cn/English/Default.asp