Speaking from actual, current, heroic multiboxing experience it's tough to make gold right now. Enchanting mats sell for almost nothing, aside from greater cosmics. You'll get enough from trash drops to pay your repair bills, and you'll get some badges as well. I think I net about 20g each toon per heroic, and maybe another 50g total in greens that I can sell or DE. So a net total of 100g - 150g for the group. If you run every heroic perfectly with no wipes, maybe you can make more. Since I usually don't sell the enchanting mats, I think I walk out of heroics with basically the 13g or whatever quest reward.

I have t9 geared DK and Shamans, and in heroics I'm lucky to pull 3K dps on trash, and 3.5 - 4K with heroism on a boss.