First you need to look how good your diet plans or ebooks are. If you are fitness guy or a personal trainer...you can ask quite a lot. I have seen professional diet plans and ebooks up to $120 per report. And that's just a short report what covers dieting and they can customize their own diet plans.
If your ebook is put together from research and free articles...you can't ask much. There are so many recipes out there, so your ones needs to stay out from crowd. You need to make them special.
I don't think these type of ebooks sell as well as they used to on websites any more.
If it was me, I would download the kindle app creator from Amazon and get the books transferred into this format and get them on Amazon. Don't ask a lot for them but build a list with the sale of the book and when you have a list, you can market to them with other related affiliate offers.
If you don't know how to do it, get someone from rent a coder or elance to do it for you.
The sale of kindles was one of the biggest sellers over Christmas and the iphone and android phones all can support the kindle app.