Paying in dollars instead of pesos for a site as a reason for not going to Mexico seems to be an odd reason to me as one poster wrote. If there is one price, ie $25 US Dollars or its equivalent in Pesos, Why not pay in Dollars? For the park owner it's a great hedge against inflation. I can understand why they ask this.
When we go to Mexico for 4 months each winter we get our cash from the money machines in Mexico which give us pesos - not dollars - we do not have dollars and it would be ridiculous for us to bring thousands of dollars in cash from the US. Where are we supposed to get these dollars to pay with dollars in Mexico?