@fjahr ASNs are incredibly easy to justify approval for from the RIRs, and cost about $500 each for the higher numbers if buying, less if the RIR is assigning them. Getting dozens of them is easy. Even easier if an attacker is willing to spin up multiple legal entities and set up org accounts w/ the RIRs.
Separately on the IP side, renting/leasing IP space in /24 blocks costs about $0.30-0.40/mo per IP when rented from a third party/non carrier. Even less cost when you’re willing to rent poor reputation IPs, which bitcoin does not care about.
I intend to spin up some ways to pull down the full BGP routing table via API (will also put the code on github, pulls from FRR, can be spun up on cloud providers that support BGP), I think it would be useful to query the full AS path of a given node and use that for warnings. In the case of what I stood up, all of the ASNs and subnets shared common AS path ASNs.