Capresso Burr Grinder (Model #551) $49.99. This is a bottom of the line burr grinder. I would classify it as descent. Not good, great, or the best, but descent. Hop on ebay and buy a Mazzer if you want the best!
I picked up a Braun off Amazon for $50 (I think you can find it less if you look aroud). Does what I need and has plenty of grind settings. Can be a little messy at times but does keep a consistent grind.
I believe it is a Braun KMM30 Coffee/Espresso Mill. Do a search at Amazon and read the reviews. This is about as cheap as you can get for burr grinders. It has lasted me over 2 years now with no problems.
Honestly neither the Braun or the Capresso that were mentioned really count as "burr" grinders. The cheapest decent burr grinder currently available is the Solis Maestro Classic from www.costco.com for $79.99. The $50 burr grinders that are prevalent in Bed Bath and Beyond, and other department stores aren't worth $5 in my opinion, let alone $50. The Capresso Infinity grinder, is a pretty decent one too, probably better than the Solis, and it retails for $99.