We slept one night by the laguna near to the main entrada and didn't like it at all. It was super noisy and there were cars running all night. Toilets are closed after 6pm and cost 3 pesos during daytime.
We slept two other nights at the spot called "Camping with Palapas & River" on iOverlander. Just follow the sign to the archeological site, you will cross 2-3 rivers. We stayed in the parking for 30 pesos per day and really enjoyed (take a look at our review on the app). Toilets are open all night and don't cost anything. Plus, the spot to swim is better, clear and clean water.
The ruins are worth to see!
Place: Lagos de Colón
Visited: March 17th, 2018
Location: 15.82631, -91.89683