As others have said, it's the same as anything you buy, whether bike-related or not. The are many different brands, many different prices, and crucially, many different qualities. And the price doesn't always reflect the quality. Over time you learn through trial and error which brands of brake pads work well. I've just burnt through a set of Clarks in about 6 weeks.... I bought them on a whim but won't be doing so again. Whereas I know from years of experience that Aztecs will get me at least 4 months, maybe 6 if I let them wear a bit more than I should. And I've heard on this forum that Kool Stop Salmon are the dogs...... though I've never tried them myself.
If you view your bike solely as a tool and are happy for the bike shop to sort it out for you, that's cool. The one thing I would say though, is if you are technically minded, most bike maintenance is actually quite straightforward once you get the hang of it, it's quite satisfying (to some) and can save you a lot of money. And from a convenience point of view, if you find you have a flat tyre or your chain needs replacing you can do it yourself on the spot rather than take it to the shop with the added cost and inconvenience of taking time of work etc.