We've featured a few retrofit motor systems on ebiketips but this might be the cheapest: the Revolution Works Revos will be funding on Kickstarter this month and prices will start at £299 for early adopters.
How so cheap? well, it's a simple enough system. The drive unit itself is a motor that sits on the rear wheel and drives it directly via the tyre using a friction roller. It's the easiet of all systems to implement, and it's not the first we've seen: Rubbee have been doing a similar kind of thing for a while, for example, but the history of the friction drive extends almost as far back as the bike itself. The benefits are that the drives are simple to fit and you don't need to swap out any of the bits of your bike.
It's not without its problems, chief amongst them being that they tend to wear through tyres quicker and they're difficult to fit to bikes with mudguards. The Revos attaches to the seat tube and drives the wheel at the top. The battery sits in the bottle position on the down tube.
Revos are offering two battery options, 100Wh and 209Wh, of which the former is presumably the one you get for your £299. Even 209Wh isn't a very big battery, and 100Wh would barely get me up the big hill home once, so it'll certainly be a charge every day kind of system. But if you live somewhere less hilly and your daily mileage is reasonably low it might be all you need.
Hugo Palmer, the designer of the system, says “Its for people who like their bike but want an ebike too, its easy to use and feels like you have a tailwind at all times. Lots of people would like to cycle to work but are reluctant because its just a bit strenuous, especially if you live in a hilly city. So Revos provides a way of enjoying a cycling commute." If you want to stay abreast of the Kickstarter campaign which runs from 16 May, head over to the Revolution Works website.