Cheapest Cardbus PCI expansion chassis I can find is from Magma, and it is just short of $1000. If you were trying to haul around a $20000 Digi system, it might be worth it. For anything remotely within the realm of sane hardware like a Delta 1010, it's far cheaper to just buy the equivalent FireWire or USB audio interface.
Personally, I like the Firewire 1814 from M-Audio, but there are plenty of possibilities that would fit your needs.