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
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.
You will have to call Ruger. You can get the phone number from their web site.