not sure what sonny is running. Probably the same as the rest of the crowd over there.
BE conversion costs are really mounts (£150 ish), driveshafts (£250) and box itself (£150). If you're not going mental with power (say 230-250lb/ft) single plate 6 paddle cable operated clutch is fine, just like you'd need on the MA box so the cost of that doesn't count. You might also need to change the speedo drive (generally buy those new from pug/cit) and they're silly expensive for what they are, about £60 iirc
More power than that, you'll need a manlier clutch, and therefore a hydraulic setup, or constella's clever cable setup.
The BE's take a bit more abuse, and I ran one at 300bhp without a diff for a while, it was quite a good laugh
Box can be a boggo standard picasso box, dragged out of any 8v 1.6 petrol engined picasso/berlingo etc. (8v version is important!)