Cost of accommodation

Sure sounds like it. $50 USD per day ?? 1000 pesos per day? 30,000 pesos per month?? Just for the A/C? That owner should be charged with usury....or something.

Why? The owner stated clearly and in advance what the terms will be if this particular renter wants to book again. To me, the terms indicate that she and her party burned the owner with a huge electric bill in the past.

Why?? Because attempting to charge a renter 30,000 pesos per month EXTRA, just for the A/C, is criminal, that's why.
And of course, the renter has the option to look elsewhere and tell the owner where to shove it. That's what I'd do.

So we've moved from "usery" to "criminal". Sheesh.

The owner obviously does not want this renter in his property again. If the owner is attempting to charge $50 USD across the board for all rentals, the market will sort itself out.

There are hundreds of units available to rent in Zihuatanejo. Pick one.