How is the water level?
I was just up there (mid February) and it was up probably about 4-5 feet compared to last summer, which isn't saying much. We stayed at Frio River Cabins (really enjoyed it) and they are about a mile North of Garner. I guess the level can depend on where you are at. We didn't go floating, so I'm not sure about the tubing.
Just went. We floated down it on Saturday. Some spots it is easy to stand, and other spots you won't be able to stand up in as it is too deep.
Do you have to pay to get into the river
Maria welcome to the forums, you usually get better responses by starting a new question. You might have noticed that the last answer was from 2014.
To answer your question - yes. While the river itself is free, most of the access is through private property and a fee is charged. The state park (which is what I use) has great access and relatively low fees. This is true for just about every river.