You're not going to get a performance car conversion for less money than you could buy a Performance Model S. Because of economies of scale, Tesla (and other car makers) can get the components so much cheaper than you can, and frankly, you're not likely to find a shop that can turn out the quality of work that a car maker can. To my pain, I can tell you that there are shops that will destroy your car in the process of converting it into a very sub-standard EV.
Getting performance out of an electric car requires a very large battery, very sophisticated components, and electronic management. You're not going to get that from a conversion shop. For not terribly much money you can convert an old junker into an EV with 20 miles of range and a top speed of 50 mph that'll do zero to 30 in ten seconds or so. Before the Nissan Leaf, there were people all over the place making these sorts of conversions. But if you want performance, stick with Tesla. They know how to do it right.