There are several factors that affect the cost of a domain name.
A Registry Operator sets the price for the TLDs that they operate.
Prices range from less than $1 to several thousand dollars per year for standard domain names.
Rights for use (or lease) of a domain names can also be bought and sold on certain auction sites or negotiated with the domain 'owners' (people that have bought the rights to the domain), on what is called the 'secondary market'. The highest price a domain has been valued at is cars.com which was valued as $872 million dollars. Actual domain sales have topped $30,000,000 for domains such as carinsurance.com (almost $50M), PrivateJet.com (over $30M), and Insurance.com ($35.6M).
Although secondary markets tend to bring the highest prices and valuations, Registry Operators may also identify premium names that carry a higher fee than standard names (though normally in the 1,000s of dollars not millions!), and these are typically short names and popular words that are searched frequently.
You can see current pricing for many domain names at https://dominion.domains/domain/pricing.
