Your price is locked in for the duration of your subscription. Rising printing costs won't affect what you pay.
Each volume is printed in limited numbers. Once a print run sells out, a reprint isn't guaranteed.
As a subscriber, your copy is reserved for all 4 volumes the moment you sign up, so you never have to worry about missing one.
This is the surest, most cost-effective way to guarantee your copy of every volume at today's price.