There is a Vimeca (Western Union) in the Playa Dorada plaza. There is also a Vimeca on the main road just past the Brugal factory. There is a cigar store in Plaza Turisol just down the main road where you can exchange money.
I THINK there is also a cambio in the Gas Station (Isla) just before the Playa Dorada.
The gas station cambio is probably walking distance. The others might be, if you are a walker.
If not, take the gua gua (B) outside the Iberostar (toward the city). It will stop in front of the Plaza Turisol or the Vimeca if you request it....for 10 pesos from the Costa Dorada.
To get to the gas station or the Playa Dorada, you have to head away from the city...or cross the road to get a gua gua in the other direction.