Insulation Dillema

[jaw22w]

Seems to be a lot of pole barn interior finishing going on. Me too. Looking at 4' wide r19 fiberglass rolls. I called my local lumber yard and asked about 4' r19 unfaced rolls price. He told me $1.12/SF. I thought that was about twice the going price per SF for 2' wide r-19 and said so. So, he says faced 4' r19 is a lot cheaper. $.55/SF. Less than half of unfaced. I don't quite understand why this would be. Must be some kind of supply issue, but that Knauf insulation is made about 65 miles from me.
I had intended to use unfaced rolls with a 6 mil poly film vapor barrier. I don't think I can get as tight a seal as I would like using just the paper face. I'm wondering if there would be a problem with putting a poly film vapor barrier directly against the paper facing of the insulation?

 

[jack stand]

Pencil it out if you built a 2' oc walls (in between the posts) and used the 2' batts. Might be a wash or small savings but give you nice wiring and airline locations

 

[jaw22w]

Pencil it out if you built a 2' oc walls (in between the posts) and used the 2' batts. Might be a wash or small savings but give you nice wiring and airline locations

I have figured costs for horizontal girts on the inside face, bookshelf girts between, and 12' vertical studs all
at 2' o.c. and the insulation for each method. It really comes out just about a wash as far as costs. I was a construction estimator for much larger projects than my little 30x40x12 barn. Since I am retired, and money is a little tighter than it used be, I have estimated this building every which way it could possibly be built. Just for the fun of it.
But my real question is about the double vapor barrier right next to each other? I think it would be OK, but I was looking for another opinion. Don't want to make a major mistake.
Thanks

Edit:
My thinking on using vertical studs or bookshelf studs is that gaps in the insulation are created by said studs. By using the 4' wide insulation, hung either horizontally or vertically, complete insulation coverage can be achieved with no breaks. I think that will pay off.
I really like the idea of horizontal girts @ 2' O.C. The only downside I see to this is that you lose 1-1/2" of floor space all the way around. I don't see this as a major problem. As far as installation, face mounted girts will be the easiest to install, then vertical studs, then bookshelf girts.

 

[dfiler2]

No problem putting poly over faced insulation, we did it all the time. Faced was used to make sure the insulation didn't settle as it would be stapled in place but we still needed a poly for a moisture barrier.

 

[Zeke]

Seems to me you'd have the benefit of having a MB on both sides. Reminds me of the sleeved insulation batts.

 

[billconner]

Paper face to interior and poly right over paper, right? I agree with dfiler2, no problem.

 

[Copymutt]

Exactly, faced is a vapor retarder, not barrier.