If you want a professional job done it'll cost you "close" to $400 for up to 30 parts.Do it yourself kits are generally only suggested for small touch up applications, but it ultimately depends on what you're looking for in a finished product, or if you just want to try something just for fun and experience. Good luck and post some pics when it"s done for us!
I guess another question that i have is how hot is the melting temps on the solder used in these older guns. I have acces to free proffesional bluing but its only hot bluing and i dont want my one barrel to come out as two or make a unsafe joint between the two barrels.
Generally, double barrel shotguns can't be hot blued using the traditional salts and tanks. Doing so will indeed ruin your gun and melt some of the solder. Usually double barrel shotguns are blued using a process called bakering which usually costs a bit more than hot blueing because it involves more work. Everyting is done pretty much the same except the chemicals used.