Hello Fawad
Nexus are DC line switches and also support storage capabilities like FC, FCoE etc. Yes they are bit pricy but the end cost would be way less as you can do many things with a Nexus switch, like creating multiple virtual switches out of a physical switch (VDC), vPC, Fabricpath and also create Storage VDCs.
4400's will be good for iWAN kind solutions or HQ-Branch designs.
Hope this helps.
Vinit
Thanks
--Vinit