For goodness sake, don't over think this. You are only here for three days, how much money can you possibly spend? Regardless of where you change your money (not at the airport, not at the hotel) you're not going to go into debt. Unless you are changing thousands of dollars, a few pesos difference here and there is not going to amount to a lifetime of indentured servitude. If you're finances are so precarious that a few pesos on the dollar makes a difference, you probably shouldn't be travelling. What would you do if you fall off a motococho and need front a $8,000.00 medical insurance claim?
Changing money is going to be the least of your problems here. Bring USD. Figure out how much you need each day. Change some money. If you need more change some more. Try not to end up with more pesos than you need. Take any unspent USD back home with you.