For full magical power, it should be set in gold. Peridot is the stone assigned to the sun. You will be able to find Peridot easily, and it should be nicely affordable. September birthdays are represented by the Sapphire . Sapphire can be found in a rainbow of colors, all but red.
Sapphires render black magic harmless, and help the wearer discern falsehoods.
Opals are usually opaque white stones with rainbow color specks or flashes that play over the surface. Opals are thought to possess the virtues of all the stones whose colors appear there. The Roman senator Nonius chose exile rather than surrendering an Opal to Mark Antony. Tourmalines are also plentiful, and medium priced. Sometimes Citrine is sold as a November birthstone substitute.