It appears that you have a Ruger Mk I, manufactured in 1978.
Ruger's web site has sn data on it.
You can request an owner's manual for free on Ruger's web site.
If it's a MK II, it will be marked as such.
IIRC, 1 in 10
Ruger made a MK III, not Remington.
50-200
Ruger has never been made outside of the USA.
$100-250, depending on the condition, type barrel, etc.
50-290 or so
You will have to call Ruger. You can get the phone number from their web site.
For this particular pistol - Mk I, Mk II, and Mk III - it is highly recommended to let a professional handle this. Many reassembly mishaps have resulted from DIY-ing it with these pistols.Contact Ruger Customer Service at the website, get an owner's manual.