Try to get the parts dept to sell you the stuff at internet pricing since you are paying the dealership to do the install. Show them that other Subaru Parts sellers are offering better pricing. Factory Subaru parts and accessories can be found at many locations on the internet for much less than the MSRP. My local Subaru parts dept always gives me better pricing. Ask for a price match.
The aluminium engine underguard, E515SSJ010, can purchased for less than $150, MSRP is $199.95.
Rear differential guard, E515EFL201, can be purchased for less than $75, MSRP is $99.95.