[A]m I just relying on industry/market self-regulation or otherwise?
Essentially, yes. Entities called Domain Registries (who are the people who oversee the day-to-day operations of Top Level Domains or "TLDs" such as .xyz) generally have most of the say over the pricing for any "premium" (newer) TLD they control.
In the case of .xyz specifically, a Registry called nic.xyz apparently owns the .xyz TLD and has control over its pricing. That Registry, in turn, is owned by a company called XYZ.
Registrars (assuming that they are a separate entity from the Registry itself) typically contract with Registries to sell a particular TLD or group of TLDs and add a small markup, as well as any "required fees". This price difference covers their own business of selling you the domain and any other responsibilities they might have.
Are yearly prices for premium TLDs universally regulated?
No, not in any meaningful way.
For "non-premium" (older) TLDs, per this Namecheap blog post:
Some domain names have fixed wholesale prices negotiated between the registry and a non-profit called the Internet Corporation for Assigned Names and Numbers (ICANN)[.] The wholesale price for older domain options like .com, .net and .biz are limited by [ICANN]. That’s why these domains are generally inexpensive to register.
However...
[ICANN] doesn’t control prices on any of the new TLD options that have appeared recently, such as .club, .shop, and .news. The wholesalers for these domain names can charge whatever they want for these new web addresses, making them subject to the open market rules of supply-and-demand and resulting in wide price ranges. [ICANN] also doesn’t limit what wholesalers of two-letter country domain options like .us and .ca can charge.
Renewals
Pricing for most common TLDs is pretty up front.
However, for newer TLDs such as .xyz, it is not uncommon to see a deceptively low introductory price and ridiculously high renewal rates (possibly thousands of dollars) simply because the Registries/ Registrars want to encourage adoption.
Simultaneously, for the Registries alone, there are the considerations that:
They typically only operate that TLD.
They are accounting for relatively low rates of likely registration.
Common generic TLDs (such as .com) are now saturated in terms of potentially available names (making newer TLDs more "valuable").
Secondary Domain Market
As pointed out in other comments and answers, there is also the issue of selling existing domains (e.g. coolname.tld) for a large price, independent of the associated TLD. These are sometimes referred to as premium domains and Registrars frequently facilitate these sales.
Often this is a one-time price (with any associated transfer fees) but some registrars will have "special renewal pricing" (whatever that might be) on these domains. These secondary sales are unregulated with the possible exception of any TLD/Registrar related requirements.
