I don’t know enough about the scene to say 100% for sure, but I think they’re pretty exclusive NJS keirin frames. They’re always finished impeccably and there are nowhere near the numbers for sale secondhand compared to Bridgestone, Level, Makino etc.
Pricewise on the secondhand market it’s Kalavinka at the top, followed by Nagasawa and 3Rensho and then the others. No idea what they cost the riders new, but they’re usually £1500-£2000 secondhand from NJS-export depending on size and finish. Plus taxes etc.
I’ve seen maybe two pop up in the UK, both on the LFGSS forum.