EVERYTHING! Just always pay in Pesos...cash or tell them to charge your card this way...unless of course their conversion rate is not to your advantage, but I haven't seen that down there other than in money exchange places, which is not advisable.
When you get the bill, it will be itemized out in pesos and a dollar conversion. The catch is that the dollar conversion is based on the "resort's" rate which was holding steady at 12.7% the entire time we were there. As you know, the dollar fluctuates every day and was between 13.4% and 14% while we were there. We told them to charge our credit card in pesos and knew we would be getting a discount for this based on the conversion rate that day being better than 12.7%. Your bank will convert it at the highest rate for the day, which again is to your advantage.
We also asked Nayeli for the wedding "bill" the day before we checked out so we could look it over and make sure it was right. She got it for us within 5 minutes and it was less than what I expected...in dollars because that is how we have been communicating the prices during the planning.
Because we had the house DJ and photographer, the bill for them was included as well. We had extra things we did with the photographer that we decided to do a week before we got there so we dealt directly with him for that and took out Pesos at the ATM!
So, when you are anywhere and are negotiating a price, do it in Pesos, pull out your converter and make sure you are getting a better price than what they initially told you in dollars. EX: you're at the market (or in a cab asking for a charge to go somewhere) and want to buy something that they tell you is $40. Ask them "How much in Pesos?" They usually go to 400 or 460 Pesos...something like that. Well, now you just went from paying $40 to $28 or $32! THEN you negotiate in pesos....How bout $350 Pesos? Etc... you just went down to about $25.
We paid the spa separately (did a ton of stuff for the wedding party as part of their gift and it was already 20% off as part of our package) We thought we'd be spending about $1200 but after paying in Pesos, we ended up saving close to $200!!
What exactly did you pay for in pesos? Was it just what was owed to the resort?