I think halacha allows that as long as you are aware of the pricing. If you were to come in without doing market research and he would add the price without explaining, this would be wrong and you could demand it back if overcharge was more than 1/6 (20 percent of normal price)
There no ona’ah on real estate, and that’s what a room rental is.
Might be a poor business decision if it annoys the customers too much, but I don’t otherwise see a problem with it.