There are already a lot of different configurations one could put together for an E-bike and make it work. The real concern for me would be the safety factor involved. If you use just any old bike frame you may be asking for trouble right off the bat. As noted in several of the threads that have been posted over the last year some bike frames are made to be super light and open the door for enherant weaknesses in frame structure and welding joints that could kill you if not avoided. I have been watching the industry pretty closely on this and since I very much value my life the first thing that I would do is conduct some research and make sure that you acquire a solid bike that is built to take a beating. Putting a high torque motor on a cheap bike frame just will not hold up and will more than likely cause injury to the rider. Also going 45mph on a bycicle in traffic is not only pretty scary, but very dangerous even for a seasoned biker. Some of the best frames I have seen are Trek, and Cannondale off road bikes. Built to take a beating and last years doing so, but also come with a comperable price range $500-$1000.
As for the elctronics there are many products on the open market today that can provide exactly what your looking for for a fairly reasonable price range. It all depends on what you plan to use it for, how long you want it to last, and how much you want to spend on it. Top speed, hill pulling torque, and overall range can be met in several ways. You can go cheap and pickup a complete kit from China (Amazon.com) for about $400-$500. But if you want to build something that will last more than a couple of months you would be better off doing more research and purchasing a solid product from a company that specializes in this type of application, and also provides some kind of warranty for whatever you buy. A really good kit will run you about $1000-$2000, plus lights, horn, mirrors, and saftey gear.
So for a really good setup your looking at spending around $3000 or more depending on how serious you want to go with your project. Considering that a lot of us have spent this much on building one really nice R/C truck to play with I would not go cheap for anything that I would put my life on the line riding on the road where many idiots drive a 4000lb vehicle. For that price you can also go in a different direction and purchase a well built scooter with everything already built in. Just my two cents, and for God sakes wear a helmet so you can arrive alive. Good luck with your quest.
Check this project out. (
http://www.rc-monster.com/forum/show...651#post419651) Notice the solidly built frame. Intended to take the torque and punishment provided by the electronics used.