Have you called around to different shops?
A head gasket on an 02 Subaru isn't that hard to do - and they're a pretty common failure, as you note.
I can see a dealership that didn't actually want to do the work quoting $1800, but an independent shop should be able to do it for $500-ish.
Are you burning oil or leaking oil? If it's leaking externally, yeah, just keep filling up. That doesn't really do anything but make a mess. If you're burning it, internally, there's a decent enough chance that the coolant passages are involve as well, and oil and coolant mixing is just a bad thing.