If your Navy Arms rifle is the lever action Yellowboy (reproduction of the Winchester 1866) they list for $400-500, depending on condition. The carbine version has a slightly lower value.
100-300 dollars
.32 short used to be available from Navy Arms or try some of the local gunshows for the Navy Arms .32 short rimfire.
50-200 USD or so
20-300 usd
That is FAR too complex (and potentially dangerous) for a brief answer here. The link below will take you to an owner's manual for a Navy Arms in-line rifle.
50-475 usd
I am not familiar with a Navy Arms Country Boy rifle- but if by chance you have a Navy Arms Country HUNTER .50 caliber muzzleloader, they are pretty much a traditional muzzle loading rifle. Remove ramrod, draw back the hammer, tap the retaining wedge pins out of the stock, then lift barrel out of the stock. Right there is a good place to stop. You can check with Navy Arms customer service through their website to see if a manual is available for your rifle. Also check to see if this rifle uses a removable breechplug. Some black powder rifles have a non-removable breech plug.
50-300 USD or so
Navy Arms was an importer/retailer. Provide a DETAILED description of ALL markings.
50-200
$500, more or less, depending on condition.
depending on condition $150 - $250