It all depends on who you contract and the level of fancy you go with the design on the house.
The most important thing to keep in mind is that legal and regulatory fees have increased a good 25% since Sept last year...
Also you must understand that Las Terrenas is not Santo Domingo or Santiago, where areas plenty of builders are pulling at each other to get your biz...
Also your choice of material for the ground floor, which means the actual home since you opted for a basic design, will play a big role in cost.
If you opt to build the house with no further potential for a second floor to be built down the road, then you could save some good money by using the smallest cinder blocks for the walls and interiors. This will translate into less cement needed to mortar...
Also your option of windows will have an impact on budget as well; by opting to use aluminum type louvers you'll cut the need of other construction materials.
Aluminum windows only require a finished cement wall to install, no special casings or anything else is needed...
There are a lot of options to go basic as basic can mean, but the big problem for anybody building in the coast is the lack of a contractor's race to offer the best price in those areas.
The golden rule is to go with somebody that you get good recommendations for...