New tubes would have to be sleeved into the remains of your barrels, which IS going to be expensive. Perhaps someone has had that done and can guess a price.

I can't tell about the butt, but it looks like it an be saved - unless it is already a replacement in which case you might want to do it a second time with better wood. It is too dirty to judge from your photos. The horrible checkering may force a replacement of the fore end wood, but let a gunsmith determine that.

Wild guesses from us based on photos will not do you much good. You need to get together with one of the restoration guys and see if they are willing, and get a ball park quotation.