I think generally speaking you could say that there are more people and more money available on the west side. Those two factors in themselves would tend to drive prices higher. There are obvious exceptions but that's how capitalism works. A consumer's job is to decide whether something is worth that value or not. Price, features, value, location, ease of purchase, are all factors that you have to weigh when making a buy decision. Even the seller's willingness to sell can be a factor. If the seller has a need for a quick sale, that may drive the price down. EVERY price is negotiable.
If you live on the west side and find a gun $50 cheaper on the east side, you have to decide if it's worth the drive to save $50. At some price differential it WILL be worth the drive and that will force the decision.