Well, I wouldn't exactly say it's in 'free fall'. Trust me, we went at the end of October after it had gone from almost parity to below 80 cents. Now that's free fall! Luckily we'd paid for almost everything up front.
You're always taking a gamble since we never know what the dollar will do. You could go buy your money today at 92 cents and it could be 96 cents by the time you go or it could just as easily be 80 cents. Calculate how much money you want to take. Calculate what it will cost to buy it today. Figure that it probably wouldn't get higher than 95 cents while you're there. Calculate the difference. Are you the type that could handle the loss if you buy it today and the dollar goes up? Or are you the kind of person who would rather pay any difference *if* it goes up as insurance against it dropping.
When we were in this situation last year, I bought half of what I expected to spend once the dollar started to tank. I was grateful when I saw the dollar hit 78 cents. But while we were there, it rose to 86 cents which was almost the same as a what I paid for it. So, as I said, it's always a gamble.