the main problem here is that you don't have enough points right now, so the webpage won't get past the point where it shows you the breakdown? If you post the exact date and flight on here I'm sure someone can look it up. I have about 240K points right now, not sure if that's enough to get past the same blocking point in the booking system.

Here are two examples:
TPA->LHR on Dec 30: Mint 225k points + $5.60
LHR->TPA on Dec 30 Mint 238,400 pts + £265.61

breakdown of fees:

Air Passenger Duty (APD) International £ 191.00

U.S. Immigration User Fee £ 5.60

U.S. APHIS User Fee £ 3.10

U.S. September 11th Security Fee £ 4.50

Passenger Service Charge - International £ 55.81

U.S. Customs User Fee £ 5.60

Total price

£ 265.61 x 1
£ 265.61