Your rifle is a Marlin Mdl 100, made for Sears under the Sear brand name. It was chambered in 22 LR, (and can also use .22 Longs and .22 Shorts) Caliber is generally marked on the barrel. It is prudent to have our rifle checked by a gunsmith before shooting for safety's sake.
Higgins rifle in caliber 22LR will run you about $95 to $150 depends on condition. Check gunbroker.com for more info...
And your question is??
IIRC, a 22lR
Try the Blue Book of Gun Values.
10-100 USD
JC Higgins RifleA JC Higgins model 85 in good to excellent condition with original box is worth about 100 dollars.
Try the Blue Book of Gun Values.
By a good gunsmith.
15-125 usd
Take it to a gunsmith for exact measurement
50-175 usd
Try e-gunparts.com