Revolutionaries and terrorists have to eat, like everyone else. They have expenses, and no armed political movement gets very far without a business plan. OK, perhaps not a traditional business plan, but at least one that makes provision for feeding the troops, arming them and seeing to minimal needs required to keep them in a fighting mood. While an angry population is necessary to get a violent organization formed, your new troops are useless without food and weapons. This is why, for example, there is no armed resistance to Zimbabwe tyrant Robert Mugabe. The population is so impoverished, and no one in the region willing to finance a revolution, that there is no way to feed and arm opponents to the government.
Every armed resistance on the planet can trace its origins, and continued existence, to someone who knows how to get the needed cash, and spend it on needed items. In Nepal, for example, the Maoist rebels need about $230 a year in food, ammo and other supplies to keep each of their fighters in action. They do this by running a large scale extortion campaign. They call it levying "revolutionary taxes" on those that can afford to pay. Thus when the Maoists began large scale operations four years ago, they needed to collect some $140,000 a month to keep their armed force going. The more money they could get, the more gunmen they could put into action. Collecting and spending this money was the highest priority for every Maoist commander. Most of their fighters were teenagers, kidnapped, then convinced, brainwashed or coerced to join the rebel forces. But the kids had to eat. Weapons and ammo had to be bought, or stolen from the police or army. Most new recruits would initially serve as porters, and laborers around the camp, while getting some training on how to handle a rifle. When enough weapons were obtained, or enough existing fighters got killed, or deserted, the new guy could be armed. Sometimes, the new recruits would go on raids without a weapon, simply because there were none available for him. During the fight, the unarmed recruit would be expected to grab a weapon from a fallen comrade, or collect one from a dead opponent after the battle was over. To put it simply, most rebel movements are low budget operations. But they do have a budget, and to survive, they must work within it.
Al Qaeda and the enemy fighters in Iraq and Afghanistan are no different. Much data on current pay rates is obtained from interrogations of captured fighters in Iraq and Afghanistan. Captured documents also confirm that, while the fighters believe, to varying degrees, in why they fight, they generally won't do it for free. Suicide bombers are an exception, although sometimes they are encouraged to volunteer by the promise of a large (a few hundred, to tens of thousands of dollars) payment to their families. Otherwise, the pay varies with how dangerous the job is in Iraq. Most of the violence is carried out by Sunni Arabs who used to do Saddam's dirty work. They were paid then, and since they got tossed off that payroll in the Spring of 2003, they expect to be paid now. The Taliban and al Qaeda come a little cheaper. In Afghanistan, Taliban fighters serve for the "campaigning season" (roughly April to September) for anywhere from $150 for $300 a month. Commanders get more. When al Qaeda was based in Afghanistan, they had a fairly elaborate payroll structure. That has largely disappeared, but it's still understood that full time al Qaeda operatives get paid regularly, and larger expenses (like travel, or weapons purchases) are covered. This money is still being raised from via Islamic charities and wealthy Arabs who believe in al Qaeda (a world government run by Islamic clerics, who will be grateful to merchants and businessmen who supported them back in the beginning.)
Counter-terrorism experts in Afghanistan are finding that the most recent Taliban offensive is being financed partly by drug gangs who are eager to see less of the police and army. Taliban gunmen can help make that happen. In this way, rebels often cooperate with drug and smuggling operations in places like South America and Asia. Rebels can't be choosers, and if riding shotgun for drug lords pays the bills, so be it.