Richard, when we travel, no matter where, we NEVER order foreign currency from our home (or any other) bank. The exchange rate sux and then they hit you with shipping costs. There is a row of ATMs near the arrival area at Cancun and any other airport. Just select a BANK ATM. Usually there's a little American or British flag to press to select English, and proceed. You will be told that there is a charge for using the ATM, just press YES, or SI, or the green button- the charge is about $1.50 or equivalent. The current exchange is just over 18 pesos/$, so 2,000 pesos (they use a dollar sign ($) so there is room for confusion) is just over $108 US. You will get the best price for everything, taxis, meals, tchotchkes, by paying with pesos.
Don't sweat having too many pesos, you will be able to use them when you leave to pay your hotel bill for the extras before putting thee rest on your credit card.
Adios! Have fun.
Jim