How much should I charge a client

First work out how many days it would take you to create this course.  (If you don't know this, we won't either.) Then work out how much money per day you would consider as fair payment for you to receive for such work. (If this is the first time you have ever done this type of work, you should be conservative in your estimate.) Then multiply the number of days by your acceptable day rate and that would give you the figure.

Your required time to create the course will depend on how long the course is, how complex the content, and how proficient you are in creating this type of course.  How much you should be paid will also be highly variable and depend on how experienced you are, how much competition there is in your marketplace, and how desperate you are for money.

All of these variables make it almost impossible for anyone to give you an accurate figure from the scant details you have so far provided.