$375 for the 2nd 5870. Not too shabby since you'll pay $400 for a desktop 5870. (of course one has 800 stream processors @ 700Mhz & 128bit bus and the the other 1600 @ 850Mhz & 256bit bus so I guess the desktop easily wins on cost vs performance)
The desktop 5870 would win even against two of the mobile 5870s in CF. The mobile ones are basically underclocked 5770s.
Of course,but some people prefer power and portability(which definitely costs more than a desktop)