Price differences on everyday in stock items can vary widely from one supplier to the other.
Recently, we bought some of those underground junction boxes, the type that look like an inverted flower pot, with removable green cover that is installed even with the grass.
We had bought 2 of them from one supplier for about $17 each. During the job, it was determined that we needed an additional one. We went to the nearest supplier (a competitor) and bought one off the self. When the bill came, it was priced out at $42!
Needless to say, we will never buy that item from them again.
OTOH, the place that wanted $42 for the underground splice box has the best deal on other in-stock items. Such as those Arlington meter box mounting blocks, or fluorescent ballasts.
Unless you get quotes in advance you can never tell who has the best price on what. It's also important to remember that no one supplier will have the best deal on everything.
That's why we maintain open accounts at all the local suppliers.