Keep in mind that you won't get that same exchange rate when you go to buy physical cash at your bank. I was checking today and call my bank to see what I could buy Pesos at. The rate online was about .046, the bank buy price was about .051.For $5000 Peso, it was about $30 US$ more to buy cash at the bank than what the online prices show. Those prices you see online are the rate that they are paying on the market for large sums of money. There are additional costs dealing with storing and shipping physical paper currency.
That said, we will be buying some Pesos in the next few days. May buy $5000 peso, which really is only about $250 US. If the conversion rate gets better, we may buy some more. For the most part we will use our credit card where we can and will get exchange rates closer to those you see online and in the paper.