Possible options for a 1:1 E-conversion?

[Unsullied_Spy]

http://montana.craigslist.org/mcy/1602718021.html

http://montana.craigslist.org/mcy/1601107980.html

http://montana.craigslist.org/mcy/1558979734.html

I want to do an electric conversion on something I can actually ride and can't find any decent go-kart frames locally so I was looking into a scooter or 3/4 wheeler. What kind of motor would I need to get one of these up to at least 35 MPH and what kind of batteries as well as distance could I get out of them? These guys have a 5kw-10kw motor for around $300 as well as a controller and what-not for it and the pricing seems reasonable if it's reliable. What kind of wattage do I need to get one of these moving with my 210 pounds riding along? Ideally I'd like something that could get up to 50 MPH or more, but I think for that kind of speed I should look into a standard bicycle as it would require less power (and less money).