I had a friend who used Lightning Source and they accepted payments via a PayPal button on their website. It was for a children's book on Amazon. I don't have their link any more, but they were making about $200 a month on their book. Hope this helps :}.
I’ve been on Kindle for some time now. If you read the comments it would seem Kindle readers are very price sensitive, voting with their feet, so to speak, by buying only books priced accordingly. Books, unless exceptional don’t often command prices above ten dollars , most sales are for books up to five dollars. Bear in mind that is with Amazon’s margin. Then 135 pages is a very small book, for adults, maybe okay for children. So for someone to buy you would need to be very well known, or have something fantastic to say. If I were you I’d look at a target price below five dollars, possibly even a taster price to start with and generate interest. Good luck, let us know your progress! :)
Establishing an opportunity to sell an ebook is not hard. If you are going to sell an ebook version of your book or if your book is strictly going to be an ebook only I would suggest that you list it on several sites. In most cases the method of getting an ebook to a customer can be relatively easy. If you have a web site already it is only a matter of establishing the method to deliver the ebook after payments have been received. Ebooks are becoming more popular today and I wish you luck on your publishing journey. Marketing is the key to the success of any book whether it is a print or ebook version makes no difference. The success rests upon the author to create an interest in the topic though multiple promotional opportunities.