If you were a Gadgeteer dude you got this here first (and still cheaper):
http://www.ghielectronics.com/catalog/product/393
and then if you are a member of the ‘other’ guys you can now get it here:
http://www.parallax.com/Store/Sensors/GasSensors/tabid/843/CategoryID/91/List/0/Level/a/ProductID/886/Default.aspx?SortField=ProductName%2CProductName
Gadgeteer leads the way and ROCKS!!! Way to go GHI Electronics as you have the other guys trying to keep up with you.
The thing which made the Gadgeteer Gas Sensor so unique and what the guys at Parallax copied is the interchangeable sensor feature as it allows you to change the sensor for a number of different gases. If there is enough interest the next step would be to build a similar gas sensor module for higher quality gas sensors such as Winsensor’s ME series or SGX Sensortech gas sensors, but these are like $100 or more just for the gas sensor.