Tell us what "not expensive" means to you and we can probably point you in the right direction. Initial cost sometimes isn't the expensive part of shoting. As mentioned the .357 Sig is an excellent round but often pricey if you don't reload. You might also want to consider which guns have high cap mags available now that the ban is off. Glock and Beretta have an abundance of these floating around. If you are not looking for a concealed carry firearm compact also takes on a new meaning, for example a full sized Glock is pretty compact when compared to a Desert Eagle .50.
Can't beat a .22 for simple plinking and range fire.