Original price of a domain: free

Next price point a bit later $100: 2 years min ($50 per year)

Next a bit later $70: 2 years min ($35 per year)

Then came competition and prices dropped.

Little known fact: The first registrars that were accredited had to certify that they had no criminal record (any of the officers) and had to be a corporation and post $100,000 bond as well as other hurdles which were all put in place by Network Solutions to limit competition.

Out of NSI came Verisign which had to erect a "chinese wall" (iirc) in order to separate the "registry" from the "registrar". Verisign of course ended up selling off NS.