Colleague recently had yet another repair on his (just out of warranty) BMW, needed new DPF sensors to the tune of £1200 apparently all in, all specialst parts not easily available elsewhere are expensive through the main dealers with few exceptions.
Your problem isn't with Subaru as such, its whether your indy should have asked you whether you wanted a pattern or genuine part fitting given the cost difference assuming they knew one was available, some indies will only fit genuine parts because they know it will work (assuming they've diagnosed correctly) first time and stay working, maybe your indy has had bad experiences of pattern parts and resulting bad experiences with customers who complained to them when the cheap part didn't do what it should for more than 5 minutes.
This is a particular problem with relatively rare makes, there just isn't the pattern part back up, i recall back in the 70s when buying parts for many cars was a nightmare, yet get a copy of Exchange and Mart and there from German and Swedish would be lists of cheap parts for Audi Porsche Mercedes BMW etc, there's never really been the equivalent of Eurocarparts or GSF for Japanese cars (nor British cars come to that)...one of our other cars is a Prado sized Landcruiser, compared to LandRover the aftermarket spares market is abysmal, but then they tend not to need much in the way of a back up industry, you pays your money and takes your choice.