I thought the other thread provided a pretty conclusive answer. Here is the official confirmation, on the Central Electoral Board (JCE) website:
Tasas para los Actos del Estado Civil
"Celebración de Matrimonio fuera de la Oficialía cuando los contrayentes son extranjeros no-residentes - RD$15,000"
(Celebration of marriage outside the registry office when both are non-resident foreigners - RD$15,000).