The most I've spent is £3500 but as we all know, that's the same as £3500 sitting there in the bank doing nothing. If I can buy an instrument ('Functional art') and enjoy it, and it holds or increases in value, why not? I don't think I'll have £3500 to play with again for a long time but I don't regret any expensive bass I've had. Technically I'd pay anything if I had the liquid funds and was confident I could sell it for the same. In fact most of my 'bass wealth' came from buying two very ice instruments at a bargain price back in about 2003, a Medulla MVP and a shell pink 1975 RI P bass.
I realise the above is about used basses and the OP is probably referring to brand new, in which case I honestly don't think I'd ever buy a brand new bass (same as with a car).