I can recommend this if all you need is 30 minutes - http://www.cyclotricity.com/front-drive-electric-bike-kit/
I've got the bottle battery version and my commute is 20 mins each way so I can probably get 60 minutes out of it.
With the LCD display you can de-restrict it and get up to 20mph just on the throttle (on the flat obviously) but I've left mine on 15mph because I like to do most of the work.
You can still get a great workout on a de-restricted bike just by using a high gear.