Domain registrars vary in their prices. There has to be some baseline cost to a registrar, on top of which they add their markup.
What is that baseline price? Is there a way to register a domain on your own without going through a registrar?
There is a non-profit in Los Angeles called ICANN with a department called IANA, and this non-profit gives several companies special monopolies on selling "top-level domains" -- those companies are, in principle, "domain name registrars". So, for example, I have the domain drostie.org; this is in the .org top-level domain, which is maintained by the Public Interest Registry.
When you want to look up "drostie.org", your computer first looks up the ICANN servers and asks, "who's responsible for .org?" and it gives a server at PIR. It then asks the PIR server, "who's responsible for drostie.org?" and it gives my web host's IP address.
So ICANN does not need to know directly, but PIR's computers needs to know. Here is where the registry steps in: PIR does not deal with you directly, but through a middleman. The middleman allows you to manage your .org domains through the same interface as your .com domains even though these are managed by different companies with different back-ends; it also in some sense reduces the sheer number of clients and transactions which PIR needs to engage in.
Thus in a strict philosophical sense you cannot avoid "going through a registrar" because in some sense PIR is a registrar -- "registry" is right in the title, even. You could try, if you were enough of a company, to do direct business with PIR, but that might set you up for numerous headaches if all you want is a working domain.
Typical prices are generally less than $15/year for a domain purchased through normal channels; Gandi and NameCheap are two popular registrars which people are usually happy with; GoDaddy is popular but has a bad reputation generally. A couple of those dollars go to ICANN, a couple go to PIR, and the rest goes to the middleman.
$10-$15 per year is a bit expensive. I doubt a domain that gets no more than 10 hits a day should pay that much. A 1000 or even as little as 100 of them owned by a single person certainly would be expensive. I wish there were a way to pay per use.
In a strict philosophical sense, the platform with the most users sets the rules. It wouldn't be surprising if an emerging platform with a lot of users established their own naming service. To some extent, the App Store is a naming service.
The people running such a platform would probably not even realize themselves the importance of having their own naming service amidst trying to get up and running. And what would have them stick with custom naming would be the same force of inertia that keeps current domain prices so high.
There's probably unseen innovation around naming waiting to be discovered.
If you needed thousands of domains you could get them for the same $15/year as subdomains, of course -- if you look up "tmp.drostie.org" the process is the same; you ask ICANN about "org", they say "PIR!"; you ask PIR about "drostie.org", they say "drostie's server"; you ask my server about "tmp.drostie.org", and it says "that's this server too!" -- I don't have to pay anyone else for that service.