According to a report in the Wall Street Journal, Verizon's plan remains the most expensive with T-Mobile on the other end of the spectrum. For 500MB of data a month with unlimited talk and text, Verizon's $80 price is $30 a month more expensive than T-Mobile's price. Over the course of a 24 month contract, that works out to $720 more for Verizon's plan. Even taking into account that you are paying full price for your handset, T-Mobile's price still works out cheaper.
source: WSJ, TheVerge via AndroidCentral