If IQ is the 1st priority criteria, price 2nd, then get the pentax M200/4.
OP did ask about cheap 200mm
I have also canon fd 200/2.8, Olympus OM 200/4 both single coating and MC, Pentax K200/2.5, and Nikkor 180/2.8 ED-IF.
Olympus and Nikkor can have reversible mount conversion to pentax K.
I may say the best IQ is in fact the nikkor 180/2.8 ED-IF, far better than K200/2.5, but hey, it's not 200mm, and costs 2x pentax M200/4.
The Olympus 200/4 is on pair with the pentax M200/4. MC version costs a bit more, but mount conversion kit costs 50 euros,
and therefore the choices narrowed to pentax M200/4 - for f4 lenses.
If you need faster than f4, get the nikkor, and buy conversion kit, or spend more $ get the DA*200/2.8
If you need low light and dirt cheap, then get the vivitar 200/2.8. Nothing can go wrong when you only spend 20usd
Last edited by hoanpham; 05-09-2012 at 02:31 AM.