This has nothing to do with the government. The airports are operated by private companies (Aerodom for instance). They charge ridiculous amounts of money for a space.. For instance my brother and I were once talking to the managers at one of the little places in STI (They sell Dominican food, beer, juices, etc...) and we asked them the question as to how much they get charged a month. The answer? 300k pesos a month just in rent. This of course does not include the other expenses (Electricity, labor, etc). Our jaws dropped...I know there's lots of traffic, but honestly I cannot see how this little concession spot can make enough to stay in business.
BTW the rent in those spaces that are past security are supposedly even higher.
Food and drinks are always very expensive at any airport I've flown through. For instance once in Atlanta my bill came to 60 USD for a burger and two shots of Whisky. 600 pesos for ONE SMALL beer seems way out of line for The DR, though. I know at STI it costs around 300 pesos, but that's BEFORE security. I've never bought anything once past security.