It depends what year if its from, since there have been no "real" changes to the mark 3 over the past decades the value I would estimate for your Ruger mark 3 to be worth, assuming its in new condition would be probably be a $320 value. if it is a newer "version" of the mark 3 then probably $360. that is the list price from ruger anyway. also barrel length may effect the price but not drastically and any accessories on the firearm its self.
hopefully this answered your question, thank you for asking.
Magazine
In brand new condition they are worth about $280.
around 200$ higher depending what condition its in
Ruger's website has extensive sn data. But the Mark III started in 2004, and is still be produced.
Best to be shown by a gunsmith.
Unknown caliber. Contact Ruger
$100-$250, depending on condition.
No such gun. Mark III is the most recent model.
marketing ploy
50-500 usd
50-200 USD
You go to the Ruger website, Customer Service, and download the Owner's Manual. There are also several Youtube videos on this.