Right, shipping could be expensive I guess, had not realised you were in the US. Ring them anyway and see how much. The exchange rate is in your favour at the moment anyway. You can also try "We Love Macs" in the US but seem quite pricey. G5 cases are easier as they will take a full size ATX, with a mac pro case you really need to put a matx mother board in. In the long run you are better using popular boards such as Gigabyte or Asus as a lot of development will have already established for these brands.
Pro's and cons:
Pro's G5 case:
Accept a full size ATX motherboard.
More space to work
Works well with motherboard tray from PC's
Con's G5:
Only space for one DVD drive
Front panel connection a bit fiddly
Power Supply position non std
Mac Pro Case Pro's:
2 dvd drives
Will accept a std PSU
Front panel a bit easier - FW800 easy but need a FW 800 card with an internal port.
4 hdd carriers
Mac Pro Con's:
Matx motherboard - you can fit a full size ATX but be prepared for some serious dremmeling!
HDD's a bit more complex to work out
Not many Matx motherboard tray's around so you need to snap out the standoffs and glue in position.
Hope this is of some help.