Hi Paul
We've had a Terrano 2.7TD 7 seat since new in 1995 and find it great for towing. It'll happily tow a caravan at 60 all day and we've never had a twitch out of it. One of the advantages of the Terrano is it's car like handling qualities. It only has the footprint of a normal estate car as well so is easy to drive around town and park. In fact my wife prefers driving it to our Corsa.
Our first caravan was a Bailey Beachcomber 470/4 as well oddly enough (which the Ranger was based on), and it towed it with ease.
The new 3.0TD versions are more powerful and fuel efficient, but I doubt that you'll find one within your budget.
I did look at Zafiras at one time as well, but realised that they wouldn't pull the skin off a rice pudding so went no further than the brochure stage. In fact at the 85% rule, the Bailey that you have is right on the Zafira's maximum limit. Quite surprising really.