oil can henrys Just the oil man, just the oil Shelton Washington

I took my Chevy van into oil can henrys to get a oil change.  The van also had a belt that was making noise.  They told me that the serpintine belt was going bad, that is why it was making noise, so I had them replace this belt, at the cost of $89.00.  About a week later the noise had returned, so I took the van back to oil can henrys.  They checked the serpintine belt and told me it was fine and this belt makes noise when it is cold and wet outside.  This is very disapointing as I live in western washington, where we have alot of this type of weather.  A few days later I take my van to a different auto repair shop and they check out this noise and find out that there are two pulleys that go along with this belt that are going bad and need to be replaced.  After the pulleys are replaced the old serpintine belt is still making noise, so they replace the belt, at the cost of $59.60 and the noise is gone and has not been heard since this repair.  I just wonder why there is such a difference in the cost of a serpintine belt and I do not think oil can henrys should be offering this service, when they apparently do not have the qualified staff to successfully complete this type of work.