It depends on where you are and when you are here. The rate has been fluctuating. The peso falls, then falls some more. The government tries to stabilize it by injecting money into the system or adopting a regulation on exchange banks. The peso gets stronger. Then it starts over again.
For sure it will be over 20 to 1, no matter what is going on at the time you are here.
But what does the exchange rate have to do with your decision? As the peso weakens, the price of many things go up. Just because you get more pesos to the dollar than before doesn't necessarily mean that you will be able to buy that many more things.
Bring the amount of cash you think you want to spend on extras. If you don't spend it all, take what is left home with you.
