The inexpensive approach is to buy a tool made for the purpose called primer pocket reamer. They are made by most of the usual suspects (Lyman, RCBS, etc.). The only issue is that when you do this by hand or by chucking a reamer into an electric screwdriver or drill is the possibility of getting an oval hole exists.
If you don't yet have a case trimmer (essential with rifle cases) the L.E. Wilson is about the best, IMHO and is under $40 at Bruno Shooter's Supply. There is a primer pocket profile cutter for it that makes the most beautiful and easily primed primer pockets on the planet. The drawback is that it is turned by hand and is a slow process. Really best for the benchrest shooter who only does a few cases at a time.
The swagers are for more volume. The only limitation to swaging is that because it works by pushing brass aside you get a very slightly raised area around the pocket that flattens back out on firing. A portion can flow back where it came from, necessitating a second run through the swager. I've never seen more than two passes required, though a second run even when it isn't required will tend to make seating easier.
RCBS makes a swager that goes on a press, as Al said. I've not used this one and hear you have to be careful to line it up with each case and be careful not to bend the tool, but Al can tell you more. Putting some dry lube on the ram apparently helps. It not be as fast as a dedicated swager, but will be faster than any cutting approach.
The dedicated tool to have is the Dillon Super-swage. If you shoot a serious volume it is the only beast to own for this task. I can do a thousand cases an hour on mine when I get into a rhythm. It has so much leverage that no lube is required. The main drawback is cost.
