I know they are heated in other markets (US/Europe), but does a 2008 Prius in Australia have heated side mirrors? I'm ordering some convex glass from ebay and they do normal or heated mirror glass: 04-09 TOYOTA PRIUS CONVEX PASSENGER SIDE MIRROR GLASS | eBay What's a quick way to find out?
If you have them they come on with the rear defroster. On a cool morning with dew on the mirrors, turn on the rear defroster. If the dew goes away in a few minutes you have heated mirrors. Or you could pop out the glass and look. You turn the glass all the way so you can get your fingers or the "proper tool" (the fastener release body tool) in there. The glass is held in a ball and socket plastic device. You have to pop out the ball (which is glued to the back of the mirror).
I wish they were, they are not heated for the UK market even though we regularly get temps of -10c or more in the winter, a real mistake by Toyota.
You can quickly try this by turning the rear defroster on and if you have heated side mirrors you should feel the mirror surface temp a bit warm when you touch it after having rear defroster on for 2 or 3 minutes. Cheers!