Comment by evanpw

The best suggestion I've seen is 1¢ for the 141st character, 2¢ for the 142nd, 4¢ for the 143rd, etc. Going slightly over 140 costs a trivial amount, but it would be stupidly expensive to tweet anything really long.

EDIT: I found where I stole this idea from: http://www.interfluidity.com/v2/6207.html