Don't know where the post is, I couldn't find it, but Norm wrote me an excellent reply some time ago when I was complaining about Pentax AF. It somewhat covered the mechanics of AF and how it relates to the lens used etc, which was very informative and it also addressed the cost factor of lightning fast AF.
We buy Pentax for many reasons, for me ...I just like the way they operate, the controls and the ease of operation, among many other factors including excellent image quality...not that I shoot much that is excellent, but I could with a Pentax if I was as skilled as others that continually post superb images here.
We also buy for value. I am currently shooting with a K5IIs and consider it a superior machine, the best Pentax I have ever owned.....and for about $500 brand new, it was more than a bargain, it was outright thievery on my part! Cost less than my little Fuji X20 Toy Camera!
As Norm pointed out, that lightning fast AF is expensive. If it was dirt cheap then every camera would be quick as a squirrel on a fresh roasted peanut! Bottom line is that you can have super fast AF anytime....anytime you want to pay for it!
I'm pretty happy with the AF of my K5IIs and I assume the K3 is at least as good, maybe better? It is the best AF I have ever used on a Pentax so far. For my $500 you won't hear me squealing!
Best Regards!