Check out the basschat marketplace, there's a Little Bastard for £300 I think, that with a 112 or similar & you'll be smiling a long time. That'll do all the valve tone you'll ever need
If you fancy the Fender/Squire P bass style, they're always coming & going on here, be patient with a bit of luck you might get a 2nd hand 50's Mexican P-bass, 2 have just been sold in the last week or so for a very good price.