does anyone sell with Amazon

Actually, I planned to self-publish to Amazon the book I am writing now, but I have doubts on self-publishing because of high cost and expenditure. I also feared I will be spending too much like what you experienced. The only suggestion I can give you is contact Amazon send them email asking about the percentage you must receive.

I am careful about postage. I use media mail whenever available. Sometimes 1st class mail is actually cheaper too. I calculate the costs before deciding to post so that I make sure I make a decent profit. I also keep light packing materials from other items I may get in the mail just so I can use to ship later packages.

You can weigh you package ahead of time, use USPS website to calculate the approximate cost of shipping. Then, when you list your book on Amazon you'll be prepared with your costs. During the listing process, when it asks you what your asking price is, you'll notice a link to see what others have listed theirs for. This is a good way to check and submit a competitive price. You don't always have to be the lowest listing either. Check the competition, maybe their used book has markings, or a missing cover. Be sure you're comparing like products. Once you've entered your asking price and proceed to submit the listing, Amazon will give you a breakdown of how much your listing is, how much shipping credit they will give you, what their commission will be and the final amount you will receive. From this final amount, you'll need to deduct the amount you estimated for shipping and you'll know what you'll gross on that book. The problem with Amazon is, some books are selling for such ridiculously low prices, you can't make a profit ... sometimes, like you mentioned, you can't even break even. If I can't make at least a little profit, I'll donate the book to a local shelter or goodwill. I'd never list a book just to break even or at a loss. Good luck with your Amazon selling!