1971
$125
H&R and New England Firearms are one in the same, NEF holds licence to the old Harrington & Richardson brand names, if it is a H&R Huntsman 45 caliber black powder single shot rifle 28" round barrel then the value is in the $100 to 125 range in 90%+ condition.
50-100 USD
Blue Book of Gun Values will help.
50-110 or so
15-150 USD or so
Consult with a good gunsmith.
$100 to $400 US depending on the condition.
25-60 USD or so
$25-$175, depending on model and condition.
Have you tried a web search? Local Library? Do a web search on Harrington and Richardson Books and you will find some sources.
25-150 USD or so