Less than $500? Nope, sorry. A Canadian company priced one for me last year at U.S.$525 - but was slow to reply to emails, so I didn't trust them and didn't order.
I've seen two versions of the waist spolier. Earlier (Outback?) wagons in the U.S. had them but my dealer couldn't find the old part # and wasn't sure if what I'd seen would fit the radius of my WRX wagon's rear naturally. The UK/Euro spoiler was the one I wanted too. Rallispec shows one for $627 (RST-9217). I think Subydude carries them but I want to say it's more than $500 - not sure though.
It's a sweet piece. I think it really sets the WRX wagon off. But at that price, I'm looking more toward suspension and other mods now.