Well, I stand corrected. I tried Google to get prices but all the prices I saw were for bulk and I immediately thought, heh, not worth it.
For an 18' length of pipe for $400 that's not bad. The other question that needs to be asked though is will the AHJ or building official have an issue with it being used as a chimney. I'm sure the pipe is UL and ASME listed but probably not for flue pipe.