K-01 with 25600 ISO but it has only LCD and AF method, new = $250-300
K-x with 12800 ISO has both methods of AF, Optical Viewfinder, and comes used only = $235 in LN- at KEH
K-r with 25600 ISO has both methods of AF, Optical Viewfinder, and comes used = $349 in LN- at KEH
K-7 with 6400 ISO has both methods of AF, Optical Viewfinder, and comes used only = $399 in LN- at KEH
Best bang for your buck IMHO is a new K-01 if you can live with the lack of an optical viewfinder and only 1 AF method. Next would be the K-x, which is a sweet little camera IMHO.
Try this comparison:
https://www.pentaxforums.com/forums/pentax-cameras-compared/?c1=k01&c2=kx&c3=kr