If you were buying a traditional crossword puzzle book, you'd pay around $3-5 for about a hundred puzzles. Based on my own experience, I'm guessing a big chunk of that goes to pay the printer, and that's fair, s/he deserves to get paid for the time and materials invested.
But there are disadvantages to the traditional crossword puzzle book: You and your friends can't compare solving times; in fact, you can't even solve the same puzzle at the same time unless you buy more than one book. You can only solve a puzzle once, unless you erase all the pencil markings and start over, but you'll see the shadow of the letters, you know you will. You can't share a puzzle you really enjoyed, unless you want to erase all the pencil markings and make a copy of it. Once you've solved all the puzzles, your puzzle book is nothing more than a highly-organized pile of trash.
Digital collections, or puzzle ebooks, are more flexible; you can compare solving times, you can work on the same puzzle at the same time your friends do, you can solve the same puzzle over and over, you can share them with your friends, and once you've solved all the puzzles, the only trash can it'll end up in is a virtual one.
When I publish a "StearsWords" puzzle ebook, the only person who gets paid is me. I create the puzzles, I edit them, I publish them, and I promote them. They're mine, and I can charge whatever I want for them.
I deliberately choose $3 for a hundred themeless and $5 for fifty themed puzzles because that's just about what you'd pay for a traditional crossword puzzle book. I'm not greedy, and I think it's a fair price, based on the number of hours I put in, creating, editing, publishing and promoting them. Interested in the math? Read on...otherwise, skip the next two paragraphs.
A daily size crossword puzzle (15x15) with a theme usually takes me a few hours, sometimes a day, depending on the theme entries; the more Scrabble-y type letters (Q, Z, J, W, etc.), the longer it takes to find fill words to cross them. But a 15x15 themeless puzzle only takes me about an hour, and most of that time is spent writing the clues.
A Sunday size puzzle (21x21) can take anywhere from a day to a week, again, depending on the theme entries, and because there are more words (~142, compared to ~78 for a 15x15), there are more clues to write. The big puzzles always have a theme, and because they're meant to be a little more difficult, I struggle with the theme entries, fill words, and clues a little more.
Now, considering that I want to make about $15 an hour (I think that's fair, it's a specialized field), I'd have to sell about 500 copies of a crossword puzzle ebook to hit my break-even point. But, since crossword puzzles have no shelf life, they never expire, and I can continue to sell the older collections while I'm making up new ones. Forever.
That's the plan, anyway.
Now, go buy one of my crossword puzzle ebooks.