What is the best rich text editor for ASP.NET web application

I have an existing e-learning web application that will contain questions, answers, explanations etc.
I am using ASP.NET platform with c# coding using MS visual studio to develop the application.
Backend database is MySQL.
The application has also images. Currently,  am handling the images by linking to an image file rather than embedding in the database. I am using this method to decrease the load on the database. But one few occasions, I need to embed simple formulas, equations etc. to have better continuity for explanations
      I have been using FreeText editor that uses FreeTextBox.dll
      There is no support now and one cannot copy images
      Therefore my current requirements for Rich Text Editor are as follows
      1. Rich Text editor for ASP.NET web application
      2. I want a solution with dll files in the bin folder not Ajax which imposes too much of load on the server
      3. Need not be free but should be affordable (e.g. < $150 per domain)
      4. Should be able to copy an image typically formulas or tables in the rich text box (RTB)
      5. If a RTB has both image and text, one should be able to extract text portion for search ( I can save the text portion in a separate field for the purpose
      6. I searched google  and found the following links
            a. http://www.cutesoft.net/ASP.NET+WYSIWYG+Editor/
            b. http://richtexteditor.com/
            c. http://ckeditor.com/
            

I am not able to figure out which one I should opt. Can anyone guide me please.