You are conflating two very different issues:
Quality of DIFFERENT models
Different models of faucets made by the same company, sold at wildly different prices, may have the same internal components that determine longevity and functional quality, with differences in pricing due to other issues such as style, outer coatings, etc. Or they may really have functional differences - e.g., plastic vs. metal components. They may also sell specific models (with minor or major differences between them) at big box stores (often want an "exclusive model" so they don't have to price-match the same model sold elsewhere), plumbing supply houses (selling to tradespeople who don't need fancy boxes but who (hopefully) care about functionality, ease of repair, etc.) and other types of retailers, including online stores.
The same types of differentiation applies across many different industries including (at times) appliances, clothing, mattresses (a classic - I remember one store used to have a huge computerized list of all the equivalent mattress models because each of the companies would private-label for each retailer, but they were mostly just different tags), etc.
It is pretty much impossible for any random person on the internet to tell you which particular models are "best", because the models change frequently, the specifications don't tell the whole story and personal preference (I may put more "value" on feature than you do).
Pricing of the SAME Model
MSRP = Manufacturer's Suggested Retail Price. The vendor (big box store, plumbing supply house, online store, etc.) can charge whatever they want. With many types of products, the MSRP is artificially high - often easily 2x the price that a retailer will pay if they purchase in volume (truckloads at a time). Some retailers will charge very low markup, hoping that they will make their profit on other things - e.g., a computer retailer might make more money on a $ 19.99 cable (that wholesales for $ 1) than on a $ 499.99 printer. Some retailers charge a fairly consistent markup (e.g., 20%, 30%, 50%, etc.) across much of their product lines. That gross profit helps to cover things like returns (which is often easy in some stores and nearly impossible in others), service, support, overhead, etc. - all of which vary dramatically from store to store.
