Your logic is wrong here. It is totally unimportant which CA you use, as long as any commonly trusted CA just checks the domain ownership using a mail address. A man-in-the-middle could simply replace your cert with that one and the user gets no warning.
> Stick with either EV Green/blue bars are a remarkable feature the user sees and might give trust. Those one are already available for $200 for 2 years. But I'm not sure if a user would realize that a MITM attack has removed the color. He wouldn't get a warning as long as any valid cert is still used. See my response above.
> or a high-assurance only If you need assurance, then yes. But a normal user doesn't care of that. And you should then also check the exact terms and conditions as well as other assurance services.