No-one in the industry calls hinges such. We refer to them as joints and they come in halves. Riveted joints are usually found on the nicer frames. There is a pointed metal pin with a flat head. The pointed end goes through the plastic and through some holes in the joint when it is cinched up then trimmed, then tapped with a hammer and doming tool on the inside to "mushroom" the end..
Price is the same if it is a three pin joint or a two pin joint.
Alternatively you may have a heat sunk joint. These are inserted in the frame by the use of a piece of apparatus that is effectively a heated pair of tongs. The joint melts its way into the frame.
On the temple (arm), if it is not pinned then it most likely part of the wire that runs through the temple. Replacing that is troublesome. We'll have to convert it to a pinned joint and you'll get the arm back a few millimetres shorter than before.
It is highly unlikely you'll break both halves of the joint assembly so the price is for one half on one side of the frame. If you do break two, let's be friends and double the price.