It would be almost impossible to list ALL the calibers for handguns. Since you're interested in economy, I'll try to list the common calibers in general order of expense. You may find sales, bulk purchases, or varying market conditions change this.
Large bores (.41/.44/.45)
This was pretty much how it stood when I deployed, at least in AZ. Market conditions may have since changed. If you want to shoot cheaply, get a .22LR. If you want to shoot the least expensive centerfire, get a 9mm auto or a .38/.357 revolver (a .357 will shoot .38s).