Generally speaking, small hobby dicemakers are one person shops: the artist is creating the dice from scratch without any of the industrial equipment or staff that larger dicemaking companies have access to. You're paying for artist hourly rates when you're paying for handmade dice, including the time it took to sand and polish the masters, create molds out of them, cast the dice set, then sand, polish, and ink the finished set as well as the experience gained by making previous dice and learning the techniques. That doesn't even include the time spent photographing dice, packaging dice, creating listings, building a website, accounting, advertising and marketing, social media, set up and clean up. Larger production companies can do that hundreds of times over in the amount of time it takes a single hobby dicemaker to produce one set because they have the advantage of large scale production equipment and more staff.
What you're paying for is the artist's time spent on producing the set. Production companies are able to produce more dice in less time, which allows them to still be profitable with a lower price point.
Other factors will influence the price of course, such as how well known a dicemaker is and a more successful artist can command a higher price. Less well known shops might charge lower to try and get sales started. The more experience a dicemaker has will also influence their prices. Cost of materials also varies wildly from maker to maker, depending on what's available where they live, so that might decrease their profit margins unless they up the price of a set. And finally, each artist assigns a different value to their time. Some artists might consider an hourly rate of $20 to be acceptable, and others might think they're worth $100/hour, which is completely up to the individual and fine either way. A higher price will turn away some otherwise potential clients, yes, but it does ensure that the artist still makes the money they want to while being able to focus more on each set they produce. On the other hand, a cheaper dicemaker might get more business for their lower prices, but would need to be able to produce sets quickly and efficiently without the quality suffering in order to meet the demand. It might be worthwhile in cases like these to actually increase the price to lower demand while still being profitable on the fewer purchases that happen, if that makes sense.
And finally, ultimately, handmade dice are pieces of art: artists sell their art for wildly varying prices all the time. If you have a budget in mind, you're bound to find some that are both within your price range as well as way outside of it.