Between 500 to 700 dollars depending on condition and location
You will have to contact barrel makers or visit their web sites to see if anyone is making them or would be willing to. Jarvis makes aftermarket "Bull" barrels for the Remington 597 in .22lr, but they no longer make the .22 Magnum barrel - I bought the last one a year ago
26"
The sizes of shells it accepts will be stamped on the barrel
Check related links to Remington Society of America for barrel date code information.
Check the Remington Society of America, date barrel codes and location. http://remingtonsociety.com/rsa/questions/barrelcodes
A while back there was a long action version of the Savage Model 12 (I think it was the 112BVSS) that was chambered in 7mm Remington Magnum. The last I ever really heard of them was back in the late 1990s. I've not seen anything about it since then. For now the only manufacturer that makes a bull barrel 7mm Remington Magnum is Remington, their Sendero line, as a matter of fact.
It will fit on the frame but the action will not function with 3 inch shells.
500.00
It depends on which barrel you need. Light 12 barrels are more expensive than the standard weight barrels. Is your gun a Magnum? If so, a mag barrel would be required with a 3" chamber. Having the correct barrel address to match the date of your gun is also important. All of this said, extra barrels usually run in the $150 to $400 range for most A5's.
Remington did not make a carbine in .44 Magnum caliber. They did chamber the Model 788 rifle in that caliber. Do you have a Ruger carbine in .44 Remington Magnum, or perhaps a Marlin in that caliber? sales@countrygunsmith.net
Check the Remington Society of America, date barrel codes and location. http://remingtonsociety.com/rsa/questions/barrelcodes
The exact value of a Remington Sportsman 12 Magnum actually depends on a couple things. Some of these things would be the condition and age of the Magnum.