I doubt the hammer-wielding tire-changer is responsible for your failed wheel bearing. They are designed to withstand constant shocking and pounding in the course of driving.
A failing wheel bearing is quite easy to diagnose if you’re a competent mechanic. Labor charge sounds reasonable. A $250 bearing/hub assembly is probably a quality part like AC Delco or National. With a good warranty. That $40 bearing is probably an “offshore” brand. It too probably has a warranty, but that doesn’t make it a good part. That just means that the parts store will give you another one when that one fails.
Don’t bring your own parts to your mechanic. The fact that he has no problem with you doing that is an indicator that he has no idea how to run a business. Don’t take advantage of his shortcomings.