If it's an older gun it's likely 1:14 twist. Most of them were.
50-550 usd
ABOUT $700
I know smith and Wesson sells them and maybe ruger. not so sure on ruger
It will be marked on the barrel. You can also call or visit ruger's website.
$500-$700, depending on exact model and condition.
It is a revolver. Value about $250, depending on exact model and condition.
I do not believe the RG 14 is a Ruger. These were inexpensive German made handguns (Rheinmetal Gemeinschaft) that sell for $25-$50. IF your firearm is marked RUGER on the barrel or frame, I could be wrong. If it is marked RG, not a Ruger.
$250-$500, depending on the EXACT model and condition.
Around $600, depending on model and condition.
You can measure the barrel yourself if you have it, using a steel tape measure. You can also contact Ruger Customer Service through the Ruger website. There is no published data that gives the barrel length of each firearm made by a given company, only the standard configuration for a given model- and THAT varies.
100-500 USD or so
100-1000 SUD depending on EXACT model variation.