Wheel Bearings

I have a Toyota Corolla 1998. Mileage is 130K. Whenever I drive it, I can hear some hissing sound from the right front side. I showed it to mechanic, who is asying that this is because of the wheel bearings. He is also suggesting that even only right side has been damaged, replace both wheel bearings in front. He is estimating it to be $400 to $500 expenses (parts close to 120$ and labor charges the rest).
I want to know whether this is true? Should I have to go for replacement of the both wheel bearings? And is the cost reasonable?
Thanks.