I like Maya Guide Adventures and they charge $50US/$100BZ. In San Ignacio, Xunantunich is a must. Also, go to Burns Avenue as it is closed to traffic and nice place to walk and eat all the delicious food of the area.
On your way to Placencia, you could stop at the Jaguar Reserve and go float the river. It's all wide spaces, out in the open, and the water is refreshing not freezing. It costs only a few dollars and you purchase your tickets at the Maya Village Center gift shop. Che'ill chocolate is located there as well and you can make your own chocolate bar.
In Placencia, you can catch a boat to Monkey River if you like a boat ride and want to see some Howler monkeys. Although they are usually at Xunantunich. I like Bunches of Fun banana tour if you like agricultural tourism.