The cheapest way to do this is if you are in the USA is to either get a free trial to Kindle Unlimited or pay for a month and then listen to the audiobooks through it. I grabbed all of the audiobooks for these titles when they went up on KU a couple year ago for $1.99 each. Amazon has slowly been raising the price on whispersync titles. They used to be 1.99 for stuff they had rights to. Now they are 3.49 or 7.49 each for a lot of them.