Opera Turbo reduces the page weight by compressing images and code through their servers. Maybe it can make you reduce your bandwidth consumption.
Also, in Opera Shift+I toggles displaying of images. There's built-in easy to use content blocker, so you can kill useless images (e.g. avatars, tweet buttons). Opera 11 added Flashblock ("Enable plug-ins on demand" in advanced prefs).
Opera CEO was at Plugg (conference) last year and he explained that Opera market share was huge in Russia and poor countries because of that feature. As for OP lot of people dont have unlimited bandwith and Opera seems to be the best at keeping the consumption low.