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I think the easiest way to get there is by ADO bus or car. The bus costs between 170 and 250 MXN pesos one way and takes 3.5 - 4hrs from Playa. Depending if you are there by car or bus I would recommend a hostel/hotel in Bacalar or more outside. Green Monkey for example is a great hostel. Or Villas Bakalar a good hotel.
If you stay at a hostel make sure you get all your food and stuff before night. A lot of the supermarkets close really early.