This will get lots of advice...
The 100mm will give you more distance from your subject for the "friendly bug" macros. I have a MF 50 and 105 and I seldom use the 50 anymore.
But I would not limit my search to just the two pentax models or even to just AF models, unless the portrait usage will me the main reason for the lens.
The sigma 70 is a well reviewed lens and a great portrait length IMHO. And the Sigma 105 and Tamron 90mm are also great lenses. Dont know if the tamron rebate reaches canada or not but it has a 90dollar rebate....
But if you just want to play around with macro to see if you are really interested in it, the Raynox 150 or 250 will clip onto your DA 50-200 and give some really nice close-up macros. For about 40 bucks!
I used one on my 50-200 before I bought my Vivitar series 1 105. And I think it is a good option if you are not really sure you will be a macro nut. If you know you really want to shoot marcros then I would snag one of the 90-105 macros...
Here is an example of the DA50-200 with the raynox 250... Believe me it takes a little practice to get one like this from the macro adaptors but macro lenses can be tough too...