We did the Auto Progresso tour of the salt marsh/Flamingo preserve/Xcambo ruins near Progresso. It was very affordable ($18/pp) and lasted about 2.5 hours.
The guide stopped at one of the salt marshes to show us how the Mayans use to farm the salt. The bus also stopped so we could see the flamingos. They were very far away so we couldn't see any details. The next stop was the ruins. Xcambo is a very small ruin but it's significant to the area because the Mayans used the salt from the marshes to trade/barter.
The bus also went along the coast line & we saw some beautiful seaside homes.
If you like history & want to see real Mexico, this would be a good tour.