I'm thinking about going there next weekend (3/15-3/17) but most hotels look booked or overpriced b/c of the marathon. Anyone have any other recommendations on places to stay?
Once you leave Moab, for the most part there isn't any private land for miles around (with a just few exceptions). There are designated camp sites along the COlorado River.
Moab also has a hostel; the Lazy Lizard if it's not booked (it may be).
For primitive camping, you can camp about anywhere other than along designated Sand Flats or the Colorado River, where you must stay in certain areas. Willow Springs Road is always a good bet.