The actual taxes combined between SXM and the USA for leaving the country are $92.90, where as they are 34 for going to STT. Unless you read the fine print you miss all the little things they get you for. If you go to STT you just pay the two US International Arrival and Departure taxes. So the difference is more like $60.

US International Departure Tax (US)
$17.70
US International Arrival Tax (US)
$17.70
St. Maarten Airport Improvement Fee (IW)
$5.00
St. Maarten Airport Departure Tax (FH)
$36.00
St. Maarten Passenger Screening Fee (FG)
$10.91
US Customs Fee (YC)
$5.50
US Immigration Fee (XY)
$7.00