That's not really the price of an IPv4 address: you don't have control over it, it's just not changing because they made a DHCP reservation or something. Owning an address means you can announce it to peers via BGP, set up PTR records, etc.

IPv4 addresses are expensive right now. Registries run out of new allocations years ago, so if you ask them you'll be put in a waiting list[1] hoping one for a block to be recovered. To get one right know you have to go on the market and negotiate a transfer: blocks are selling at ~50$/address right now. The price more than doubled in the last year or so: people are even speculating on it [2].

[1]: https://www.ripe.net/manage-ips-and-asns/ipv4/ipv4-pool

[2]: https://teddit.net/r/investing/comments/qdple3/i_am_planning...

Your ISP probably hasn't tried to acquire IPv4 addresses recently. https://ipv4.global/reports/ shows prices around $40/address, so it would take 2-3 years to break even at $1.30/month.

(Although, people rent apartments with break-even periods well beyond 10 years, so maybe 2-3 is still fine.)