Al Qaeda, like so many terrorist organizations in the past, is degenerating into a purely criminal organization, with the religious and political goals of the past used as window dressing, and little else. Such an evolution is inevitable, if a terrorist operation lasts long enough without achieving any of its goals (like overthrowing a government, or founding a country). Al Qaeda peaked with the September 11, 2001 attacks. After 2003, the Islamic terrorists suffered serious damage to their image (in the Moslem world) in Iraq, where the slaughter of Moslem women and children destroyed most of the popularity the terrorists had achieved in its previous attacks on Westerners. As al Qaeda's popularity fell, so did the number of Moslems willing to give money. But it got worse, as the U.S. began having more success convincing Moslem countries to crack down on the Islamic charities that were basically fund raisers for Islamic terrorists. At the same time, American pressure on the international financial system made it more difficult for the terrorist organizations to move their money. Using cash couriers only put more key people out there where they could be spotted and caught. In a word, al Qaeda is now broke, and reduced to begging and making desperate appeals via the web.
It's long been known that al Qaeda encouraged its members to raise money any way they could. One of the easiest scams has been to steal from Islamic charities. Sometimes these charities give the money willingly, sometimes unwittingly. Another source is, or mostly was, wealthy Islamic conservatives who are willing to contribute directly to terrorist groups. This last angle is less popular now, especially in Saudi Arabia. Arab governments are cracking down on such contributions, now that these attacks are happening in Arab countries. Some of the donors are also discouraged, as they felt the payments provided immunity from terrorist attacks. Many Arab banks are also helping to track, and freeze, terrorist funds, either voluntarily, or under pressure from the larger international banks (who are being advised to do so by the United States.).
As a practical matter, terrorist organizations are held together by cash. Al Qaeda, during its Afghanistan heyday during the late 1990s, had a large payroll, and an annual budget of up to $30 million. This is known from captured and prisoner interrogations. While the pay was not great (there were a lot of email from field agents pleading for more money), it kept a lot of people in the game.
For all the big numbers tossed around, terrorists do not appear to have a lot of cash to work with. And in Iraq, a lot of cash came from Saddam Hussein supporters. Saddam had billions of dollars to play with, that much is known because of captured records, and over a billion in Saddams' cash that was found shortly after the 2003 invasion was over. Subsequent operations uncovered more documents, and other evidence, that a lot more of that cash was still out there, and some of it was being spent to keep Sunni Arabs fighting Americans. Some of the cash got to Syria, where a lot of it entered the banking system, and found its way to other al Qaeda operations. Prisoner interrogations revealed that a lot of the people planting bombs, and ambushing convoys in Iraq were being paid. It is thought that some of the Baath Party (Saddams' power base) money is also going to other terrorist organizations. But it is now known that most Islamic terrorists outside the Middle East have to pay their own way.
Some of the Saddam cash is still in play, paying for some of the few terrorist bombs that still go off in Iraq. Most al Qaeda (or affiliated) terrorists, because education and skill levels tend to be quite low, find crime is often the most attractive option. Kidnapping, extortion, drugs, theft and credit card fraud are favorites. More and more al Qaeda members, at least the ones already so identified, are being caught carrying out these gangster activities.
Al Qaeda has always had a problem with members getting distracted by things that money can buy. Theft and misappropriation of funds is a constant problem, and that was made clear when so many al Qaeda documents were captured in Afghanistan during late 2001. Those problems have gotten worse since then, as the quality of the recruits has declined, while the chances of getting caught or killed have increased. The line between terrorist and gangster has become blurred, and that's a trend that will continue.