If you only need a hammer drill occasionally, perhaps you could get by with this Mastercraft hammer drill adapter. After chucking the adapter into your drill, you activate the hammering action by holding onto the adapter while you operate the drill.
The adapter requires a drill with at least a 3/8″ chuck. If you want to use the adapter with a cordless drill it should probably be a 12V or higher model. Canadian Tire retails this hammer drill adapter for $25. And for some reason, Duluth Trading Company charges $35 for their seemingly identical version.