Steve Manning, author of How to Write a Book on Anything in 14 Days or Less, has just offered an easy payment plan. You can buy it in three installments. Check out the details at http://www.writeabooknow.com. In the box where it says "comments", just write in "3 easy payments, please." Steve, a real person, will make sure that you get the easy payment plan even though the order will still say the full amount.
If you have been having trouble getting your book written, Steve's book can help.
If you have a higher-priced product, you might try offering a payment plan as well.