This summer sterling dropped to historic lows making Britain a bargain for meeting planners, but long-term fluctuations are hard to predict. Some foreign providers are open to negotiating a lock-in rate to protect you from currency swings, and others, including Argentina, will accept U.S. dollars for hotels.
Talk to a tax advisor before you pick your destination. Most European countries refund VAT (value added tax, also known as IVA in Latin American countries) but Turkey does not. Mexico gives an instant credit for U.S. passport holders, but if your meeting destination doesn’t refund VAT make sure you include that tax in registration and other attendee fees, otherwise you will pay it out of your own pocket.