You could try and find a Zoom B3 and an expression pedal which would give you plenty of options.
You can certainly get something like a Line6 PODxt Live for less than £200, the amp models are better than the B3 IMO, but the effects aren't as good. You also have to allow for buying the Bass Expansion Pack.
If you can stretch the budget, you can get a Line6 HD500x (again, budget for the HD Bass Pack), the amp models and effects are far better than the B3 or PODxt, and it's a great choice (use one myself, big fan of the HD500x).
If you just want effects, then you could look at the Line 6 M13/M9/M5, no expression pedal included though.
The Boss GT6B or GT10B are solid choices.
Take a look on the For Sale Section here, eBay etc., there's some good choices out there.