Tulum consists of a sleepy little town with shopping and restaurants and a couple of miles of beach-front cabanas and resorts along the coastal road. You can either stay directly on the beach or in the town; a lot of places in town offer bikes so you can ride to the beach. Most tourism revolves around the ruins, but the Eco Chic/Yoga retreat trend is starting to take hold on the beach. Reasonable rates can still be found, though you may have to haggle a little and do some searching. Overall, this is a safe and relaxing place to visit, and is pretty much the southern border of the tourist driven economy in the Mayan Riviera.

If you don’t book ahead of time, you will find that sometimes prices are negotiable. However, this will depend on how busy the season is.
There are a few backpacker cabanas where you can stay in huts on the beach with no electricity and communal bathrooms for around $40/night. However, Tulum beachfront is becoming more popular (Eco-chic, yoga retreats and the like), so these types of lodgings are becoming rarer. Staying in the little town of Tulum is probably your best bet on a budget, and the beach is within walking distance.  Hostels are available from about $10 and up.  There are also a few camping options in the area.

Eco-chic is the word of the day, and there are some beautiful options for beach-front rooms and cabanas for less than $100/night.

An option just north of Tulum is the Blue Sky Hotel. It is located just past Cenote Manati (named for the manatees that used to visit), which is next to Casa Cenote (another hotel option that we have not tried).  The cenote literally ends at the road and goes underground to meet the sea.  In Sept 2011 The Blue Sky Hotel had just been purchased by new owners who are planning renovations.  This was a wonderful place with a pool and killer restaurant.  Casa Manati is off the beaten path; it is mostly a residential area and therefore very quiet with little ambient light at night.  The reef is extraordinary and the snorkeling is fabulous.  The hotel has kayaks for guests to use to explore.  The cenote also offers good snorkeling.  A suite with 2 bedrooms and 2 baths and an expansive balcony overlooking the ocean was reasonably priced, though prices may have gone up.

Blue Sky Hotel

There are many spa options, with less of the resort feel you get from the, well resorts.  The properties tend to be smaller, though there seem to be quite a few options for luxurious accommodations.  Keep in mind that many of these will have minimum stays.

The area between Playa del Carmen and Tulum is packed with all inclusive resorts and spas that can meet any of your needs.

We visited El Dorado Seaside Suites and it was a truly fabulous option for those wanting to get away from it all.  Adults only with swim-up rooms that connect to swim-up bars, private nude beaches, and at least five restaurants on site.  There are several Karisma resorts along the Mayan Riviera to choose from.