I just replaced mine in my 04. As you probably have found, the R160 rear diff with the right gear ratio for manual transmission Outbacks can be harder to find than those with automatics.
I found one at a local salvage yard and paid $250. I also found one up near Canada for 50$ but I'd have to pull it from the car and drive up there. It was worth the money to me to get the local one for more money.
That said, there's numerous rear ends on ebay. Find out what gear ratio you need and go hunting. Mine had a 4.11 ratio on my MT 2004 OB.