If you go to the Service/Parts page on the Remington Society of America there are a lot of places where you can find places that can help you I've included the link below. However bolts are typically restricted most will not sell a bolt to anyone directly it must go to a gunsmith/FFL because of the liability issues with fitting/headspace etc.
http://remingtonsociety.com/rsa/service
100-300
100-400 USD
100-400 or so
It could be that you have a A-bolt hunter model I,But I am not 100%certain.I can say that your browning bolt action rifle was made in the year 1979 by the two letters in the serial number(RN).
It will be marked.
codey
made in belgium
Good luck. I would try gun shops, gun shows, want ads, Shotgun News to start.
Yes 3006, 270 is a long action 308, 243 is a short action.
$800-$1400 depending on the figure in the wood, blueing and pitting from salt damage.
At least 500 dollars for one in the condition that you describe.
Quite simple really. Wrap a dollar bill around the barrel at the muzzle end and slide it back toward the action. You should get no resistance as the bill passes between the stock and the barrel and it should slide easily all the way back to the action.