An E1 visa is not as concerned with the investment as it is with the trading. An E2, however, would normally require around $100,000. You would not change the visa if inside the U.S., but rather, your status. You would have to contact the attorney to determine costs. The proof and documentation for a successful E1 or E2 is extensive and you should contact the attorney directly.
Brian D. Lerner
Attorney at Law
Retain an immigration lawyer to discuss the process if you are not familiar with it.
You can make an informed decision once all the facts are before you.
There may be other visas available to you and you should consult with an immigration attorney to explore your options.