If you suffer from budget creep (like most of us do) you might find some facelifts around your budget, and they all have a 6 speed box.
There were three straight 6 options, 2.5i, 2.5Si and 3.0Si. But the 2.5i has 40 bhp less than the 2.5Si - I think it was intended as a replacement for the 2.2i.
The best thing about the facelifts is that they are all slightly more powerful, but they also came in SE and Sport trim and the Sport models had the very sought-after M-Sport seats as standard. Only downside is they have an electric water pump which will die at some point causing overheating within a mile, and new OE pumps cost around £250/300 so long as you don't buy from BMW! People often fit a new one as a preventative measure, but if you find one that has already had one that's a bonus.