My rule of thumb is to pay in the currency that I'm quoted in. If you pay in the other currency, they will have to do a conversion and the rate they will use will not be in your favor. Hotels quote in dollars so that's how I pay them. Most stores will quote in colones. MP's that quote in colones, so use that. The only exceptions vare HLH and New Fantasy. Their prices in colones are higher than dollars, so better to pay in dollars.
As for the girls, they will take either. 500:1 exchange rate will work, i.e. $80 or ¢40,000.
You can exchange money at the airport,
UPSTAIRS on the departure level. Go outside arrivals and cross to the garage and go back up into the terminal. There is a bank (red square booth) on the right side as you walk in. They give true rates. The exchange windows in baggage claim rip you off for like 11%.
Read this newbie thread:
viewtopic.php?f=11&t=16357