Well
My no-holds-barred recommendation would be a Fylde Magician (absolutely beautiful instruments), but you wouldn't get near one of those with your budget!

I've had a quick Google and Ibanez make some cheap ones starting at under £200 that will probably be alright, but stepping up a bit in price there's Tanglewoods and Washburns available. I haven't had my hands on a Tanglewood or Washburn acoustic bass, but the price/performance ratio of their other guitars suggests they'll be good.

No substitute for going to Denmark Street or somewhere and having a look/play though. Bigger (volume) bodies will give you a bigger and deeper sound, but don't expect them to keep up with acoustic guitars playing just acoustically - they're not usually loud enough. Pickup quality is something important to consider as well, since I guess you'll be spending most of your time playing through an amp. Piezo pickups are fine here although I wouldn't typically recommend them on an acoustic guitar.

Playing wise it will be something akin to transferring from electric to acoustic guitar, or bass guitar to double bass - the strings will be a hell of a lot stiffer and will knacker your fingers til you get used to it!

I've also just read a website which offers the excellent tip to try and find one with a hard case chucked in, as finding a suitably sized one separately can be an arse!

PS - I'd say what you are looking for would be called an 'acoustic bass guitar'.

@ darras - there's many sorts of pickups, and they all perform differently depending on what sort of guitar you put them on, and particularly how much stage noise there is. I'm not a huge fan of the Takamine style soundhole pickups, and on a quiet enough stage (solo artist etc) would definitely use a microphone. Recently, for more band style setups, I've been gravitating towards a Fishmann Rare Earth/Aura system which works bloody well, considering I'm not usually a fan of DSP trickery on acoustic instruments.
(Son of Sam-i-am We're all as mad as hatters here, Mon 15 Dec 2008, 11:11, Reply)