two words for you...
EEEEEE bay
although it won't necessarily be cheap.
I assume you just want a trigger stick and not an analog trigger stick.
The tron casing style goes for mondo bucks... but if you watch ebay simliar sticks can get through for cheap (i.e. xenophobe, even gorf... maybe some zaxxon clone or something)
Why not hack one your self if you're that cost conscience? The raider pro trigger stick hack is documented enough that by now they come out looking pretty nice. *Shrug*
good luck!
Rampy