Let me add one thing to all the great advice here (comes from experience...the greatest teacher!!!); When you buy your corded drill make sure it has some real power behind it. I was using auger bits to drill out doubled up top plates when running wiring conduit (smurf tube) for my theater during construction. My poor little Craftsman half-inch drill just didn't have enough torque for anything over a half inch auger bit to get through the header. Unless you want to burn up a drill, get one big enough to do the work. Or.....you might want to consider renting a big right angle drill made specifically for this purpose. The right-angle adapter you linked to isn't gonna cut it for larger sized holes using a auger bit.
Well, I just bought the drill and adapter, both at Lowes. Hopefully this Dewalt will get the job done. Come on...it's a Dewalt. I got that and a Dewalt recip saw....I'm feeling all professional now.
*Throws a blanket over his old ryobi cordless drill he's had up to now*