Give $400 - 500 in food to a food bank. Or give that much to a church or homeless shelter. Give it to the Wounded Warriors program, or the Fisher House.
Normally I would say to try and pick up a M1 Carbine to go with your Garand, but I agree some of the previous posters that you have a pretty big hole in your (nice) collection. I would pick up a S&W, a Ruger, or an older Dan Wesson .357 revolver. You will be able to find a nice used revolver that is within, or close to your budget.