I guess you are talking about the lower trim on the bottom of the bumper cover on the side, part # 88975681. Holy bleep, that is ridiculous! I saw it for $107 plus S&H and I agree, that is crazy for a small piece of plastic.
Best I could recommend is look on
http://www.car-part.com" onclick="window.open(this.href);return false; to see if there are any GTs around you and see if you can get the part used cheaper. Or look on ebay for someone selling Vibe GT parts and ask them about it.
Good luck!