Looking for a retail version (grey disk).
Not wanting to spend a lot as I'm simply upgrading an older secondary iMac.
Maybe $15-$20?

where are you located?

It can still be purchased from Apple directly:
Mac OS X 10.6 Snow Leopard - Apple Store (Canada) (http://store.apple.com/ca/product/MC573Z/A?mco=MTY3ODQ5OTY)

If you want a retail disc, you do NOT want a grey disc. Grey disks are system-specific. Retail discs are white, with a picture of a snow leopard on the front.
http://farm3.static.flickr.com/2603/3872097851_3e188cffb5.jpg

Ah! Thanks.
Must of had a brain freeze and confused the two. Much appreciated.

xorpion, I'm in downtown-ish Toronto.

+ 1 Thanks! I've been looking for a used copy because I figured this was EOL at the apple store. Never assume, eh?