About 1000 to 7000 kcalories per stage, e.g, Jens Voigt averaged 300 W for 3 hrs 54 minutes with 50 minutes of that at 370 W
during Stage 4 of the 2012 US Pro challenge.
http://home.trainingpeaks.com/athlete/workout/QT2EVB6IVPCKIGOCHUJWN5OLUM
Cancellara averaged 285 W for 6.5 hrs during his 2010 Tour of Flanders win, although he is big (82 kg).
Here is some TdF stage power data :
http://velonews.competitor.com/2013/07/tour-de-france/pro-power-analysis-stages-18-19-at-the-tour-de-france_296653
Here's a really high power output from one TdF stage winner :
http://www.srm.de/news/road-cycling/le-tour-de-france-stage-18/
Many Tour de France stages are ridden at lower power outputs though.
Many amateurs can TT near professional (or even better) than many professional cyclists but long road races and multiple stages with long climbs and altitude in the mix in grand tours or the classics is a different matter.