One of the online booking sites will give you a good idea of airfares. They're easy to locate on the www. The yucatantoday.com website is a good resource for that part of the country, and there are a couple of good online/print guides.
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Join Date: May 2000
Location: NorCal - SMF area
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It's difficult to say without any idea of budget preferences, etc. to make any recommendations.
But your options to Mérida are many, now that Mexico has LLCs (and MX is down), and for a longer trip there is even the deluxe bus service (e.g. ADO Platino or ADO GL - Gran Lujo with onboard IFE and Wireless, etc.) (It's a nineteen hour slog, so air is definitely more practical.)
As JDiver mentrioned, budget information would help us provide some ideas. Just returned from a few days in Merida. It was a pleasure as always. You can find food and hotels to meet most budgets and desires. What is it you are looking to do?