How much will your electric bill be?
My friends in Cancun pay anywhere from USD $20 a month to $200 a month depending particularly on how much they use their air conditioners. So.. the REAL answer is more technical...
In 2006 electricity was selling for 2 pesos per kWh (kilowatt hour). That is about 18 cents U.S. So... here is how to calculate things: a coffee pot for example is marked 1,000 W on the sticker or 1kW. That means if you left it on for exactly 1 hour it would eat up 1,000 Watts and would cost 18 cents to operate.
A window air conditioner running constantly on Hi/Cool probably uses 1,700 W. Now we know that it will cycle on and off once the room becomes cool, so let's say it will use an average of 1,200 W which is 1.2kW. Running it for 8 hours will cost 1.2 x .18 cents x 8 hours = $1.73
A further example... a window fan uses 80W. That works out to 0.08kW (move the decimal place to the left 3 times). So running it for 8 hours costs 0.08 x .18 cents x 8 hours = $0.12 or 12 cents.
One of the those new spiral type light bulbs uses 15W. Leaving it on for 12 hours would cost... 0.015 x .18 cents x 12 hours = less than 3 cents.
For those REALLY on a budget, if you keep your electric bill under 800kWh in an 8 month period you will get a major reduced rate on the first 330kWh or so. That's why your Mexican neighbor is paying 20 bucks electric for 2 months and you are paying $300.
Bottom line? Take it easy on things that eat up electricity like coffee pots, air conditioners, and God forbid... an electric clothes dryer.