Considering what is an expensive bass, you'd also have to factor in inflation rates etc. A bass that cost £1,000 new say 10 years ago would cost a fair bit more now (don't know the numbers, but it will be more).
Though I would say that a "premium" bass would cost between £1,000-£2,000, and "premium plus" (i.e. "expensive") would be more than £2,000.
What we also need to factor in is that new, "inexpensive" basses are better quality than they've ever been.