To me, expensive means paying more than you need to.
So I'm firmly at £1,000 as that's where the law of diminishing returnd really kicks in. These days you can buy a bass perfectly capable of the standard required for any stage in the world for comfortably under £1k. I paid over that for a couple of basses and a couple that would have been more new. The extra pays for things that aren't actually necessary that take them into the realm of being luxury items where you choose to pay more.
25 years ago or more, you had to pay proportionally a lot more to get something of the quality you can get for £500-£750 these days.