Hi. I want to hire someone to produce a simple app that would send the user a daily message of inspiration from my book. The app would also have a link to purchase the book the quote came from. But I have no idea how much to offer for such a service.
Impossible to estimate. Everyone calls their job "simple" or "easy" but even a 1 page app can be complex. What you describe doesn't sound complex, but never underestimate a client's scope creep superpowers.
My advice is to pay someone to flesh out details including your ideas, what you want, and maybe technical specifications if you want it built specifically for a platform. Get as detailed as possible. Then, use this document to present to developers to get an estimate from them.