Where the money goes
Book marketing costs fall into three buckets: tools (email software, a landing page), paid reach (ads and paid promotions), and help (courses, communities, or freelancers). Time is the hidden fourth cost, and for most indie authors it is the largest.
Book Profits Club, which publishes this guide, suggests judging every cost by what a reader is worth over time, including later books and any coaching or speaking work, not only by one sale.