Everyone is told that selling online means you don't need shelf space so your overheads are less. Now let's consider for a moment that most offline product developers don't retail their own products, they make deals with retailers who stock their stuff on their limited shelf space and take a big chunk of the profits in return.
So we invent a product then make deals with the people with shelf space (hint: that's the affiliates with decent lists) who take a chunk of the profits in return for putting our product in front of customers.
Now go read everything you can find about getting products into stores and you've just learned nearly everything you need to get your products on to big lists and it won't cost you the massively over priced "Internet" version of the same information.
If you really want you can send me all the money you've saved from this tip ... I won't mind.