Subaru just quoted me £135 + vat for one, but I got a Bosch one from Mill Autoquip for £41.20, I did get the LS05 universal though, part number is 0258986505. This is a four wire version with a plug kit, strap the fourth wire to earth if your car is 3 wire. On the computer it does not show against Subaru but is the right part. Do not forget to test with the gas analyser after!
Other part numbers are:
0258 003 254 for a 3 wire version
Subaru OE is 22690-AA500 94-2000