ugh... I've had bad issues with USB wireless cards... low power and range sucks.
check out these auctions:
Might be really of interest:
http://cgi.ebay.com/ws/eBayISAPI.dll...tem=2082567591
Also check out these:
http://cgi.ebay.com/ws/eBayISAPI.dll...tem=2081771437
http://cgi.ebay.com/ws/eBayISAPI.dll...tem=2081796171
http://cgi.ebay.com/ws/eBayISAPI.dll...tem=2082362223
http://cgi.ebay.com/ws/eBayISAPI.dll...tem=2082064449
Searching for variations on these might yield cheap results as well.
Additionally, before someone complains that ISA cards are ****e and shouldn't be used, remember that PCMCIA *is* ISA (16-bit ISA interface)... Cardbus is a 32-bit PCI interface, and there *are* many ISA/PCMCIA wireless 802.11a cards out there.
In any case, these can give you some cheap solutions if you just want to hook up 2 computers for the purpose of transferring files.
You can probably find PCI adapters that are not 802.11 for really cheap too if it must be PCI.