If southern Canyonlands NP is booked up, Hamburger Rock is a great no-frills option only 3 miles from the entrance.
Hamburger Rock is a small BLM campground with 10 sites based around an interesting rock outcropping. Each site can accommodate around 6 campers, 2 tents, and 2 cars. The bathrooms here are very basic, open-top pits, and no other services are offered. Camping fees are only $6/night.