RIRs only handle transfers of /24s or larger. I suppose it might be possible for a "legacy" pre-RIR address holder to reassign ownership rights of a single add

RIRs only handle transfers of /24s or larger. I suppose it might be possible for a "legacy" pre-RIR address holder to reassign ownership rights of a single address, but I've never seen it happen for anything smaller than a /24. Even if it did happen, the addresses would be unusable on the Internet, since it's common practice to reject announcements of anything smaller than /24. Your friend (correctly, IMO) values his address block more than the market does. They're regularly selling for $5000-6000 these days.