There are two varieties of the 1930-S quarter, known as the "Type 1" and "Type 2" varieties. The Type 1 variety has a smaller S mint mark, while the Type 2 variety has a larger S mint mark. The Type 2 variety is more common and therefore less valuable than the Type 1 variety.
The 1930-P quarter is also available in a proof finish. Proof coins are struck specially for collectors and are not intended for circulation. Proof 1930-P quarters are typically worth several hundred dollars.
The value of a 1930 U.S. quarter can also be affected by its provenance, or history of ownership. A quarter with a well-documented provenance may be worth more than a quarter without a known history.