Having been involved in the setup of a Publishing Company I agree that Printing Costs are actually quite minimal. The reason it costs so much for books is the stitch up the shops/online shops have made of the market.
A 300 page Novel printed in B&W and say 10,000 copies costs around £1.50 once shipping is included, now if you went for a million it can drop to as little as 60p per copy. The issue is that Amazon etc.. want on average a whopping 55% of the Retail Price for themselves.
So if your book is £8 it's £4.40 to Amazon then possibly £1.50 for printing and then if you are using a publisher they only give you 10% of the Retail Price so with all of that in place the Author gets really hammered.
Using E-books should sort this out if people just self publish and cut out the huge fees to publishers and get it edited by an independent firm and use something like Lightning Source who can put work onto E-Book via Amazon at a mere 20% gouge of the Retail meaning the Author gets a lot more per book and can cut the price right down. But without a Publisher marketing a novel is very expensive, so the price goes back up.