I am looking to book two one way tickets, JFK-SJU. They are 9,800 miles per ticket and I have a total of 18,300 points, so I will have to pay extra.

If I buy just one, it uses the miles and wants $5.60 for taxes. Sounds good.

But if I buy two together it comes to $78.90, with $16.50 for the tickets for the extra 1300 points (apparently split between the two passengers per the numbers below) and then the following taxes, over $30 per ticket. It seems like I am having to pay all the taxes on both tickets. Do you not have to pay the transportation tax and PCF on a total free ticket, but you do on a discounted ticket? If so, maybe transferring some Chase UR points over so that both seats can be free would be worthwhile. Or just buy them separately and only pay the higher taxes on one ticket (although usng th UR points could be worthwhile since it saves me significantly on the taxes).

Here are the numbers (per ticket and total):

Base fare $8.25 $16.50

Taxes, fees and charges
U.S. Transportation Tax (International) $21.10 $42.20
U.S. September 11th Security Fee $5.60 $11.20
U.S. Passenger Facility Charge $4.50 $9.00
Total price $39.45 x 2 $78.90