Buying real estate in South America with US dollars? how to exchange?

Im trying to buy a house or apt in Colombia, I have the funds in US dollars but they only accept pesos, how do I send the money at the best exchange rate with little or no sending fee, I dont want no western union, its expensive and they pay bad, maybe I can use a bank or other entity, PLEASE ANSWER ONLY IF YOU KNOW ABOUT THIS BUSINESS OR HAVE DONE SOMETHING LIKE IT BEFORE, thanks