Yeah you can get them a bit cheaper if you shop around a bit, I'd expect to pay around £170 to £200 for a new one. They're what makes the cambelt service on a 24v 164 rather more expensive!
Yeah, apart from the Ferrari part number (which took some finding) that's about the only thing I found out about the 24v cambelt service, that it was expensive
Good job those tensioners are quite robust...
I did find out one thing which might make an interesting project though - the later type 24v tensioner fits straight onto a 12v block (though won't fit the 164's 24v), and that takes the cheaper 12v water pump too. So if it was possible to fit the early 24v heads onto the 12v block (they're too expensive / rare for me so haven't tried) it might be possible to make an engine which uses the more common, cheaper 916 GTV-on tensioners and 12v water pump, which would potentially knock about £150 off the cost of servicing.
Edit: Thinking about it, the position of the 12v oil pump drive would mean it fouled the camshaft sprockets, so that wouldn't work unless you fitted an external dry sump type oil pump, at which point it wouldn't be worth the bother.
BTW I've heard rumours the early type 24v valves are no longer available from some people, is that true or another one of those Busso 'urban myths', like the unavailability of the tensioners?