This has been periodically dropping in price on Amazon every few months, and it just hit one of the lowest prices it's been (ships from and sold by amazon.com):

amazon,com : Samyang SY24M-P 24mm Wide Angle Lens for Pentax : Camera Lenses : Camera & Photo

There's also a note that says, "Get 20% back on amount charged to an Amazon Prime credit card" which sounds like an extra good deal for people who have that.