You can buy them new for around $400-$450.
If yours is a nicely old 3-screw model (pre-1973, I think?) then it's likely worth a bit more. It's not known as a "collectible" example of a handgun. They are a lot of fun, however. I love mine.
If you paid $300 or less for it, and it's in terrific shape, then you did well. If you paid $300-$400 and it's in terrific shape, then you did okay. If you paid more and/or it's beaten, abused or neglected, you did not do well.
If you bought it as an investment, something you hope or expect to appreciate in value, you probably missed... by a wide margin.
If you want to invest, don't buy firearms.