I'm trying to decide whether to invest the time and effort required to compete with Aaron Wall's SEO Book. I am trying to get a decent idea of ROI. I have a decent idea of the Investment required, but not of the Return.
That's a tough one, since Aaron's book is so well-known. I have no magic formula to help you. You need to estimate how many copies you'll sell and figure out the net price you'll get per copy... but that's obvious stuff. If you already have a highly targeted mailing list and/or customers then it becomes easier to estimate this stuff. I will tell you, though, that if you're doing it strictly for money then e-books are much better than printed books. A normal printed book done through a standard publisher will net you between $1 and $2 per copy. A half-decent e-book will net you between $20-$50 per copy depending on your selling price, so the money is much better.