The actual cost to get the plane in the air for 100 miles is a minor part of the fare. Wanna know why it cost so much to fly between SJU and EIS?

Start with emplaned passenger fees (each way): SJU - $23 EIS -$20
US International departure tax $13.40 Arrival tax $13.40
SJU Facilities fee $4.50
Federal Security Segment Tax $5.00
Customs Fee $5.00
Immegrations Fee $7.00
Dept of Agriculture Fee $3.10
That comes up to $124.00 that the carrier adds to the round trip ticket plus the $20 you pay to get out of the BVI!
In addition the airlines pay Landing fees:SJU - $4.50/ton GTOW EIS $4.00/ton GTOW
Counter, gate and ramp space rent and at least 3 or 4 ground support personel.

And somewhere in there there has to be a little profit to justify being in an industry as crazy as air travel.