I would like to be able to sell my text book to my students in e-book format. I know there is the kindle store that takes 65% of the sales price, which is in my eyes too much. Are there any e-book stores for teachers and professors that provide their service for a fair price?
Fairness is a difficult question to answer. You need to ask fair to who: the publisher, the author, or the students. Publishers provide a number of services (e.g., editing, typesetting, printing, and marketing). It is fair for them to get paid for their efforts. Obviously it is fair for authors to get paid for writing. It is also fair to expect students to pay for high quality learning materials.
The question then becomes what is a fair price to charge students and how much of that should go to the publisher. The fees charged by many publishers depend on the number of copies sold since they have some fixed costs that they need to recoup and some costs that scale with the number of copies sold. If you think the service being offered by the publisher is unfair, you can always self-publish and do the editing and marketing yourself.
As for the selling price, this really depends on the quality of the book relative to other similar books. That said, in my opinion selling your book to students in your class is unethical since the students are already paying for the teaching material indirectly through tuition and fees. I don't think of it as being different from selling lecture slides, notes, and exam keys and in the limit if you just want to make money from your students you could just sell grades.
The rate charged by the vendor depends on the price: the 65% rate usually applies to books costing more than $15 or so. Below the threshold amazon charges 30%. Apple's iBooks charge 30% for all prices, and so provides a cheaper option with a similar service, as long as everyone uses the apple's proprietary hardware.
Personally I would reconsider your pricing to a more reasonable level. As self publisher you get a much larger slice of the profits, and in my opinion academic textbooks are priced excessively. If you cannot give the book away as others have suggested, then the other factor is that a low price would encourage more students to buy outright rather than share, and you also remove the second hand market, thus having many more actual sales. With this model students pay less to learn and you probably earn more money, and in a sense everybody wins.