Don't go for a mazda B2500 - it just drinks deisel :evil: I've just filled mine up today (full 'cos I've got a long journey to make tomorrow) and it cost £75 bl**dy quid!!!
If you do find one, consider a petrol instead of deisel; petrol costs less and a petrol engine can be converted to use LPG which a deisel can't.
The usual types you'll find on the market are Mitsubishi L200's. They are big and wallowy on the road, but are very powerful and comfortable to drive. Expect to pay around £5k for one with aprox 80-100k on the dial.
I've heard that the Vauxhall Brava pick up is good... one of the chaps down the lottie has a crew cab one for bails of hay for his horses, and the Toyota Hilux is very popular too.
How big is the stuff you are thinking of carting to the lotty? if it's just a few tools etc then why not consider one of the smaller car-type pick ups like the skoda felicia pick up. I had a skoda a couple of years ago and it was great - always started first time, easy to drive and being a skoda was as tough as old boots!