Al, I bought mine without the OS (optical stabilization) as it was $1800.00 VS. $2500.00 and the Pentax bodies have the IS (image stabilization aka anti shake). Using both can have the systems competing with each other and actually cause blur.
I purchased mine used at
www.keh.com for $800.00 and later had to send it in for repair due to catching a basketball in the lens. So total I am still under $1000.00 outlay for the lens.
Keh.com had a few of these last time I looked in the $700.00-$1000.00 range.