Original horn-rimmed glasses are made of horn or tortoise shell. So they are not cheap. But later, a thick plastics was designed to replace those materials in order to decrease the cost.
Compared with metal frames, horn frame is featured by its simplicity. However, it is prone to break as you attempt to install lenses.
As for less money for horn-rimmed glasses, online shopping has been proved effective every time. You can go to the optical store with your father. And ask him to try different styles. Remember the brand and article no of a glasses that is your father favorite. And log on ebay, where the price is lower.
But be careful there would be fakes. Do not buy that price is too lower. And when you get the glasses, have the shop assistant distinguished.