If you can get an OEM one, they should be under $10. But currently, at "retail/Resell" prices, they are around $33 each.
Places like
Avenet-Marshall and
Newark should currently have them. Search for "HACA-0001"
Mike
P.S. Dropping the fan to 5V isn't hard to do(find hte 12V wire, disconnect it from mb header, connect to 5V power supply wire.
The arcticoolers performance may drop tremendously with a reduced fan speed as these guys tend to run warm with a 12V fan.