Fair deal for author

[Paul]

I'm working with a poet on a prayer book for children and families. That is, the poet is writing an English text; it will also have Hebrew text that is in the public domain, and some transliteration of the Hebrew into Latin letters for which I hold the rights.

We're really doing this for local use, but the plan is to publish it through CreateSpace and offer it to the public, in the hope of earning at least the out-of-pocket costs. I will be the publisher, using my existing CreateSpace account. Copyright of the English text will be in the name of the poet.

If or when those costs have been covered, what is a fair royalty to the poet? CreateSpace per-copy royalties (to the publisher) vary according to the sales channel: highest through the book's own web page, less through Amazon, and still less through other book vendors. Because of that, I'm thinking that a percentage of the net, rather than a per-copy royalty, might be better.

But what percentage? And would it be reasonable to limit the term of royalties? Neither of us is young and I don't want our heirs to have to deal with it until the copyright expires.