It depends on many things. How much you want it, how much you need it, how much money you have.
Ernst
Dear Ernst,
Seconded. Implicit in what you say, too, is the question of how much you are willing to sacrifice in order to pay for a single expensive interest. Old car restorers are a prize example. They often spend far more time and money on their vehicles than Leica users spend on Leicas -- and surprisingly few of them are rich men.
I know quite a few professionals who use Leicas for most of their personal photography and some of their professional work, and can therefore 'lose' the VAT/TVA/MwSt and write the camera or lens off against the business. Many more, in fact, than rich twits; but I don't (usually) move in rich twit circles. There's also the point that being rich does not automatically make someone a bad photographer, any more than buying a Leica will automatically make you a good photographer.
The most I've ever spent on a lens was $3000 on a 1938 Thambar 90/2.2. These command silly money from collectors but since buying mine I've found that there is a surprisingly big band of users. I borrowed it for an article, expecting to say, "Yes, very nice, very interesting, but not worth the money" -- and then I bought it... I've never seen another lens that gives the same results.
Those who say "Leica buyers have lots of money and want to show off" puzzle me.
To whom are they supposed to be showing off? Most people don't know what a Leica is; if you move in circles where a Leica is a plaything, no-one is going to be impressed anyway; and the idea of buying a Leica to impress the local camera club strikes me as pretty weird. Weirder still to try to impress people on the internet, in which case you might as well lie anyway: have I ever mentioned my collection of Leica prototype Noctiluxes...? From the reaction of some people on forums like this, I'd think that the level of bitching, sniping and sour grapes you get from a handful of the disaffected would be a
disincentive to buy a Leica.
What's the most I'd spend? Dunno. I hope I haven't spent it yet. But a lens has to be pretty amazing for me to spend
anything on it: I've got most of what I want. If the M9 hadn't come out, I might have bought the 24 Summilux, but again, I might not. All counterfactual conditionals are true.
Cheers,
R.