The cheapest stick of 512 3200 that I recognized the brand and also had decent reviews (on new egg) was a stick of mushkin. I think kingmax and kinston with decent ratings was around the same price (around $78-80). Memory is outrageously expensive now. The cheapest decent looking sticks of 512 are in the $80-100 range as far as I have been able to tell. I saw the crucial labs guy posting so I went to check out crucial. I believe the cheapest stick there was $99 and cas l of 3 not very detailed specs otherwise.
Then I went back to look more at new egg. As I looked up the memory from lowest to highest, the individual sticks of 512 with lower latencies rapidly approach the price where if buying two (2x 512) the matched pairs aren't all that much more than buying two individual sticks of 512. I read comments saying that buying matched pairs is really not necessary. Some write that if you want "matched" pairs just buy two singles at the same time as they should theoretically have been manufactured around the same time and so forth.
I would ask some more questions and see what people recommend for your usage. I am doing the same. Ram is crazy expensive although it has come down just a bit of late. I don't want to spend $50-140 extra if it isn't well worth it in durability and performance. Also, of course, it has to work with what I want to use it with.