The elaborate Margarita stand is located to the left of the main structure in Epcot's Mexican Pavilion. They offer "on-the-rocks" and "frozen" margarita's along with a couple Mexican-ish beers and a cocktail. The stand also offers two or three food items. While there is a very well designed cue area, there's really not much in the way of seating or standing close to the booth. You'll have to walk a little... but there are uncovered standing and seating tables here and there.
(*) Price ranges listed are the average cost for one main entree and one soft beverage item, unless otherwise stated. There are many combinations of appetizers, deserts and drinks that will add to your final total. Many parks also use seasonal pricing systems which result in food and beverage costs increasing at peak times. Please check with the location that you are interested in for specific pricing information.