Maybe this will help.

Hunter Arms would factory fit additional/new barrels to Smith guns for 1/2 of the MRSP.

Figure out (based on the condition of the barrels) the selling price of the whole (same grade/quality) gun and ask 25% of that.
Watching Smith barrels on e-bay, 12g 00 Armor steel extractor barrels, which would be fit to a $500-700 gun in similar condition, are SOLD (not offered) for $150-$200.

https://sites.google.com/a/damascusknowledge.com/www/home