One last point that is a factor in our region of the country is cold water diving, which calls for equipment designed to work in lower temperatures, especially when ice diving. Quality of construction is another factor, but for the most part a minor one. By and large, there is no junk in the US made regulator market. The liability of building products with defects is so high, that manufacturers take a lot of time and care, although some manufacturers have more recalls than others. Warranty and service is a big factor.
Some manufacturers offer lifetime limited warranties.
This means that as long as you follow the requirements, typically annual service by a factory authorized service center, they will cover all parts and you pay only labor. Also, the service work in place is a factor. Does the manufacturer require that people selling their equipment also be trained in it's service. Yes, dive stores are typically more expensive than mail order, they have to be. They have trained sales staff, they send off technicians to school for repair clinics, maintain parts inventories on equipment and do a lot of other things all of which costs money.