The smallest routable IPv4 network on the Internet is a /24, which is 256 addresses. Regional Internet Registries won't assign you smaller than a /24, but individual ISPs might. Even if you have an assignment, maintaining it requires payment of annual fees to your RIR, unless you're a lucky "legacy" address holder from before the RIRs were formed.
I own a /24 from the early 90's, registered before ARIN and the other RIRs existed. It is considered a legacy block and I've never signed the legacy registration agreement, so no fees for me! I do have it routed to my home network over a "business broadband" connection.
Jealous! I pay ARIN hundreds of dollars a year in RSA fees.
As a legacy address holder, how do you feel about RPKI?
I use my network mostly for experimentation and it is unlikely to be a target for hijack. If I were a commercial enterprise I would want RPKI for the future. Currently it seems mostly irrelevant in a practical sense, due to the small number of ASes actually validating.
From what I understand, the problem is in routing them. If you could buy a single IP address then all the routers need to keep a record of where that IP address goes to rather than a simple rule of this whole block goes out port 5
Pretty sure youd have better luck purchasing a perpetual license to one from a top tier owner.