I too a few months ago was considering ordering either a cordierite or fibrament stone from online sources. Then somewhere I came across that a cordierite Kiln shelf (stone) is essentially a cordierite pizza stone without a FDA sticker. So I started calling local pottery ceramic supplies stores, and found at least two local sources for cordierite. I wanted a round 16 or 15 inch stone, they had 16x16 but that wouldn't fit in my weber kettle, so I settled for a 15x16 octagonal 5/8 thick good up to 2000+F, for $18 plus tax.
I have been using that stone in my Weber Kettle, Weber Gas Genesis Grill, and my electric oven. The stone in the kettle has had occasional fire flame directly touch it with no problems, however it is not recommend for application where direct flames touch the stone.
Personally, I chose to not pay freight and have to worry about shipping damage or what to do if the stone cracked after a few uses. I know for $18-20 bucks I can easily replace the local source stone.
As a added NOTE:
I think reading November's post
on comparing the two types of stones, should also help to make a final decision