It's a Ruger Standard Auto Pistol, produced from 1949 to 1982, when it was replaced with the Mark II.
Yours has been "rode hard and put away wet". There is almost no finish remaining, and it shows considerable pitting. Also, unless you doctored the picture so as not to show it, the serial number has been removed.... it should be stamped in front of the ejection port on the right side of the pistol. I'm not sure, but the authorities may take a dim view of posessing a firearm with the serial number removed.
Given the condition it's in, I doubt it's worth $25.