Food for thought.
I am inclined to purchase a book, to support you.
I really enjoy the puzzle ( on most days ).
However I find playing online very desirable ( with record keeping, online dictionary lookup, and so on ).
If you were to include a PayPal 'Make a small donation' button, I would be inclined to show my appreciation that way, rather than buy a hard copy book.
You never know, many hundreds of small donations might build towards a nice result.
Michael