As a rough rule of thumb, take what you think would be reasonable for a bass guitar and multiply it by a factor of three.
Cheap and cheerful model - £400-£1000
Half decent - £1,000-3,000
Getting serious - £3,000-£8,000
Silly Money - £8,000+
Does that help you at all?
(Someone please suggest better price brackets for this if you disagree, I've only ever bought one bass)