Yep, the bulbs are spendy, but they really do upgrade a Maglite. A 3xD cell light with a regulated LED is a pretty good light.

The 3 Watt TerraLux TLE-6EXB has a lot of throw when you tighten up the beam. Without these I'd have put my Maglites into deep storage; instead they fill a role that a 2xAA light cannot.