According to information published IPv4 Global, a IP address auction service, the price of IP addresses between August 2020 and August 2021 has more than doubled.
Their data shows that at the end of August 29, 2020 the price per IP was $23.24. As of August 29, 2021, the price was $47.50.
IPv4 Global handles auctions, escrow, and related transactional services for IP block auctions. For example, you can buy a /22 in ARIN, a /23 in RIPE, etc. The fact that they handle so many IP address transactions gives them an excellent base of data upon which to draw trends.