The rapid growth of the internet has exhausted the IPv4 protocol. The Internet Assigned Numbers Authority (IANA) globally manages the IP address space, the regional internet registries (RIR) manage assignment. Four of the five RIRs have effectively exhausted their allocation blocks.The alternatives for acquiring IPv4 addresses are not ideal, such as costly third-party marketplaces, long waiting lists with RIRs, and complicated mutually agreed transfers.

The average price of an IPv4 address in 2018 was around 17 dollars, an enormous number when compared to the average of just around 6 dollars per address in 2015. In 2021 prices per IP address are expected to be around 25 dollars per IP or higher if purchased in smaller blocks.

See ARIN recent report below that shows 15% more requests than actual transfers during   September and October of 2020 which provides further indication that demand is high and supply is low, which will lead to increased IPv4 prices in Q1 of 2021

 
See the ARIN recent report above that shows 15% more requests than actual transfers during September and October of 2020 which provides further indication that demand is high and supply is low, which will lead to increased IPv4 prices in Q1 of 2021
The larger blocks show a deeper bottom at ~$5 per IP in 2015, followed by a quite linear rise to $23 per IP for /16s, and $26 per IP for very large blocks, by the end of 2020
The smaller blocks did not linger at $5/IP and rose quickly to $20 per IP by 2018, where they plateaued for 18 months before rising of late to $23 per IP