I'm amazed some of you don't know how to shop around for cheapest Blu-ray movies. Amazon.com sells them really cheap if you keep checking and also other sellers behind Amazon sells (blu-ray boxset.com or something I think) them for like less than $20 or so. Also go to Blu-ray.com forum, some sellers have movies for pretty cheap also they have thread on hot deals. That's where I check there often. It saved me a lot of $$$.
I got several movies for $17 or less. I got Starship Trooper Blu-ray for $12 new.
You just gotta keep checking because prices changes all of the time. Last time at Tower.com they were selling Dark City Director's Cut for Blu-ray for $10! I missed it.