Wow, it doesn't even include things like the airport facility charge either! You are likely to be hit with a massive charge when you collect the car.
What dates are you hiring the car from, will see if I can work out an estimated cost and see if its better off you just booking the car somewhere else.
At the moment I will just guess its a week in June. I reckon you will have to pay, on a Midsize rental:
$175 young driver surcharge
$12.50 facility charge
Airport access fee circa $70
$5 license fee
CDW and Extended protection (This is the insurance you need - extended protection gets rid of big excesses etc) $37 a DAY so $259
So thats $520 of crap. Oh - then sales tax on top of that. So $570ish. £380.
Lets price the SAME Midsize car for the SAME dates with the SAME hire car company - Alamo - but using a reputable UK broker like uscarhire. The prices quoted by uscarhire include EVERYTHING you need - all the insurance you need, zero excess, all fees and taxes included. Using the Young Driver Package it includes the surcharge as well.
£229. You could even hire something like a Mustang Convertible for less than you'd pay in fees at the counter for your 'free' rental!
It's difficult to fully estimate the charges involved when you get there with your package booking. My figures are only an estimate. You wont know for sure until you stand at the kiosk.
But given that the young driver surcharge ALONE is £115, I'd be amazed if it wasn't much cheaper to simply pretend you dont have a booking and buy a new reservation from somebody like
http://www.uscarhire.co.uk.
Essentially, we British get unbeleivable deals on US car hire when booked and paid for from the UK. Most places offer totally inclusive packages at rates US citizens can only dream of.