My lbs has these (or something very like them) going for fifty quid (that's the only link I could find on the subject) - machined out of one block of aluminium, startlingly low weight.
I've got a TA aluminium cassette in the shed. It didn't wear out in two rides but I took it off as I couldn't put up with having to change down two and up one.
The plot thickens...I popped by the bike shop and the owner says it's titanium; it certainly looks like ti, although I'd assumed it was aluminium because it was made in one chunk. There are also at least some shifting ramps - front and back.
So - did anyone have one of those crazily priced SRP ti cassettes back in the day, and how did THEY last? This one is scarily light - it doesn't feel right when you pick it up, the hand-eye-brain thing doesn't work.
According to Poshbikes, ti cassettes wear badly - but they do a custom coating service....
There's got to be a demand for these with you weight weenies - they're so light I could bring back a suitcase of the things!