Like many others I decided to quit waiting for a decent electric road bike at a reasonable price, so I built one out of a spare bike I bought off eBay for about $700. I based mine on a '82 Yamaha turbo because 1) I have the ICE version (hence the spare), 2) I like that it is fully faired so it looks 'normal' and 3) it's a shaft drive and one of my main goal was to make it as maintenance free as possible. Shaft drives weigh a lot more and are not as efficient as chain drives, but they are maintenance free. Here is a picture of the finished product. Like Stryker (who built the 72 volt version) I live close to work so distance was not an issue, but speed and performance were, as I have over 3 miles of a rather steep curvy road to go home on. One big thing to consider when doing this is the finished product. Like Stryker I am using AGM sealed lead-acid batteries because of convenience. But since I like the final product so much my goal has always been to upgrade it to some Li-Ion or Ni-MHyd batteries as soon as the become commercially available. It would shave 100 lbs off and give me twice the range, so it's an investment worth making.
Step 1: First, find a donor bike
I have an 1982 Yamaha Turbo. It looks like this. I also had a spare-parts bike (that I bought off eBay for ~$700). It was, for the most part, complete but in pieces.
I decided that I was probably not going to use the spare-parts bike for anything so I stripped it.