I believe we we paid $3 for an hour in Novemeber. There was another rate for a longer timeframe, but I can't remember the details. Maybe someone will have a better memory on this. My husband has taken to calling me Dory lately (as in Nemo). LOL
We just bought an innertube at Target for $2.99 that we plan on using for our upcoming trip. We did the same thing 2 years ago and it worked out great!
One thing I did notice is that the tubes provided by BC/YC were clear. I don't know if they would require you to have a clear one but if you have a choice you might want to choose a clear one.