Sounds about the right price, I am doing a hg job on my wagon right now too so info is kinda fresh in my brain...though I tend to have the memory of a goldfish.
You will probably want to do your rear main seal and oil separator plate (metal)<----dealer item only..and take a look at your clutch and flywheel if you have standard transmission. I'm sure the cam seals and support o-rings will be included but keep the mechanic informed if he is not a Subaru tech. You will need the headstuds replaced too as they were likely stretched out of specifications.
Most of the seals and gaskets are hopefully included with repair but take a look at the hg replacement gasket kit sets and note that everything is there and the mechanic is notified of these parts and that he guarantees his work. I have heard too many times that mechanics that aren't familiar with these motors will overlook some things. These motors though very reliable after the hg jobs are still pricey to work on because they must be removed from the car which = lots of hard earned cash.