Not going to buy it, but I think the installment plan makes a lot of sense, both from the point of view of the customer and from Monte's POV.
For Monte, I see three options:
1) Offer the book for sale in a year. This makes money off the people who would buy it then.
2) Offer the book for sale now, with a full-price preorder. This will make money off the people who would buy it in a year, and give him an early influx of cash from the preorders. However, there are probably not that many people who would give him $120 now for a book in a year without some serious incentives. He could discount the book for preorders, but then he runs into problems making a profit.
3) Offer the book for sale now, with a low preorder and the monthly payments. This way he gets the people from 1 and 2, and in addition grabs everyone who wants the book but can't/won't pay $120 in one shot. "It's only 10 a month!" managed to grab a lot of people. Not to mention, he also gets the advantage of an early influx of cash that is guaranteed consistent for a year.
From the buyer's POV, you can either pay 120 in a lump sum in a year, or trust Monte to save it for you. In return for giving him money early, you get extra benefits over someone who bought the book when it was released. Everyone wins.
I don't see it as "so expensive as to need an installment plan", I see it as "Monte knows economics and is trying to maximize his market." Good for him.