IMHO, when you look for work like this and assess an offer you need to ask yourself how much the exchange rate would need to change for you to quit, how likely it is to happen, and how to plan and prepare for it. You should also perhaps assess whether the exchange rate is currently on the "low" or "high" side. But, again, you need to accept +/-10% as unavoidable over any given year.
Would you like to protect yourself against the dollar tanking down? or would you like to take advantage of a potential dollar recovery?
Either way, in salary negotiations: Ask as much as you can get away with.
If you just want stability then negotiate your salary in your local currency (but if it gets too expensive you may be let go anyway)
Anyway, more than anything take into account all the taxes you'll have to pay locally.