What is shopping like in Playa del Carmen, Tulum Mexico?
Electrical and electronic stuff is typically 10 to 25 % more expensive in Mexico than the USA. They do have good options, but definitely not in the Tulum area. You might have better luck in Playa del Carmen or in Cozumel (short ferry from Playa del Carmen.) Cozumel is a Tax Free port and it does have good selection of itmes. Nintendo DS games will be available, but I do not think the selection will be big. In Mexico I have seen that they modify the game consoles to accept copies of games. But Playa, Cozumel and Cancun have stores specializing in Games. Beware the compatibility of any electrical/electronic items. Things like voltage, plugs, TV signal mode, DVD region, etc. might give you a headache. Good shopping option in the area are perfumes, watches, some jewerly and precious stones, but as alwasy you have to be very careful that the item is authentic. Have fun.
