I got a full kit from BMS Battery to try out eBikes due to a breathing difficulty, whole shebang cost around £280 inc shipping (though I think I was a bit lucky on the Customs duty, which should have added about £50 as far as I can see). Cute 100 250W motor, 10ah Li-ion battery, thumb throttle, charger and controller. Really delighted with it so far, attached to one of my road bikes. I use it relatively sparingly, always on uphills, on flats when tired or into a headwind. Using it thus I can get 50 miles plus from the battery, though of course this would decrease sharply with heavier use. The only drawback is the slight drag from the motor when riding without power, but this can easily be overcome with a faint feathering on the throttle - and when I put my normal race wheel back on for a flat ride it feels like I'm flying!
As far as fitting's concerned it was a complete doddle - battery and controller into an Oxford handlebar bag, cable tied throttle onto handlebars (too large diameter to fit as intended), cable tied all other wires snugly and that's about it (I didn't bother with the supplied PAS or brake levers)! The only mod I had to make was filing down my front fork dropouts slightly to fit the motor axle, but they're still (importantly) working fine with the original wheel. A slight problem is changing a tube on the front wheel if I get a puncture when out and about, what with the cables tied to the forks, but I've solved that by using some old velcro ties (the sort one gets holding computer cables bundled etc) instead.
Thoroughly recommend it to anyone, I must admit I was a bit of a snob at first, thinking it would be a stopgap until my health recovered, but when/if it does I'm definitely going to get a second bike, probably a hybrid, to put the kit on for commuting, shopping and general fun and have my race bike for full on workouts. The only mystery to me is why pedelecs aren't more popular, I think if more people knew about them so many more would cycle commute/shop/tour...a world without cars and just eBikes quietly humming around, it'd be bliss!
P.S. Has anyone heard anything about the proposed Shimano STEPs kit? Great publicity at the end of last year and now seems to have died a quiet death, are they still going to put it out?