Online Travel Booking and Bidding Agencies - Priceline type sites departing anywhere but U.S.A.?

Does anyone know of sites which allow you to name your own price for flights departing other places of the world. If anyone has detailed info for a site allowing this for departures from Canada or Mexico i'd greatly apreceate it. But it'd be interesting to know if it exists in other places as well.
Thanx

http://www.priceline.com.hk
http://www.priceline.co.uk

I found one which is Mexican based although they seem to offer starting U.S.A. as well:

www.preciobase.com (http://www.preciobase.com)