I can't give you an estimate, but maybe I can help you figure out what it takes to build a wall so you can do some calculations based on costs in your area.
I'm assuming you have 8' ceilings. If they are higher, you might need a bit more material.
1. Studs are 16" OC (on center). How many studs will it take to span 12'? About 10. You'll need a bottom plate and a header so add on 4 more for good measure. Oh, and nails to put it all together.

2. Drywall comes in 4'x8' sheets. You'll need 6 (3 for each side). Don't forget the screws, tape, mud, and sand paper.
3. Doors cost anywhere from $15 for a cheap hollow core to $$. Don't forget the hardware, handle, and trim.
4. Paint
5. Is your floor going to be affected by moving the wall? If so, will you have to patch/repair/replace?
Not sure if that helps.