John in NM
I don't think that is a standard size, is it? Usually I see it go from 4" to 6".
Second Mark's suggestion of using thin wall pipe for this, it's cheaper, lighter, and plenty strong enough for this.
You could also look into spiral steel ducting, the times I've used it I found the price very reasonable. Trick with that is finding a supplier (preferably the manufacturer, in which case it should be competitive with sched 40 PVC - at least it was 20 years ago ). When I lived in Tucson there was a company that manufactured it, they would happily sell you 10' or 10,000' in whatever diameter you wanted.