Useful info (exchange rates are approx based on when I travelled to Central America - April 2015):
Out of the 5 countries I visited, Costa Rica was the most expensive, but Antigua in Guatemala wasn't far behind.
El Salvador adopted the US dollar as their national currency some time ago.
1 US dollar = 500 Colones
1 US dollar = 26 Cordobas
1 US dollar = 20 Lempira
1 US dollar = 7.5 Quetzales
I was chuffed to get a 1979 white dollar in El Salvador and looked it up to see how rare it was once I got back home. Turns out it isn't that special (would have been great to get the 1981 version), but still a good little find for the currency collection.