Actually, the £300 is total, thankfully. VA said they charge £270 to process your pet(s), +£10 for any additional pets (so £280 for total for my 2 pets). Then, if your pets are unaccompanied, they charge another £295. (I'm not really sure why, since I would assume you'd have to meet your pets at the airport in the UK anyway, and it's not like they can travel in the cabin with you, so technically they're "unaccompanied" either way...guess that's government for you, though.)
Oh, and the $175 VA handling fee seems to be regardless of how many pets you have as well.
So, it adds up pretty quickly, esp. if they're flying solo, but at least it's only £10 more for extra pets.
(Obviously, you may want to check with DEFRA and confirm these fees, though I would think VA would know their stuff if they do this all the time.)