I feel as though to top something like "Cracking the Coding Interview", you're going to have to get close to the breadth they cover for the price they charge. You mention they 'charge' $25 which for sure is more than your $5; however, they've got loads and loads of questions for each data structure.
Currently, you're selling each question for about 35 cents. Although that's super cheap per question, $5 for 11 questions somehow doesn't seem like a great deal. However, I think people will be willing to pay the same for a larger database of questions e.g. I would be happy to pay $25 for 80 questions).
Currently, you're selling each question for about 35 cents. Although that's super cheap per question, $5 for 11 questions somehow doesn't seem like a great deal. However, I think people will be willing to pay the same for a larger database of questions e.g. I would be happy to pay $25 for 80 questions).