LONDON (REUTERS) - The militants who killed 130 people in Paris, triggering waves of air strikes on Syria and security alerts around the world, may have spent as little as around 7,000 euros ($10,000) to stage their attacks.

World leaders scrambled to crack down on terrorist financing after the Nov 13 assaults, which have been claimed by Islamic State in retaliation for strikes on Iraq and Syria.

Within days, France and Belgium announced €1 billion worth of additional security measures.

In contrast, the attacks themselves, requiring little more than Kalashnikovs and ammunition, homemade suicide belts and rental cars and apartments, were a reminder of how little it takes to kill indiscriminately and sow fear and confusion.

The Sept 11 attacks on Washington and New York cost between US$400,000 and US$500,000, according to the independent 9/11 Commission, a sum that covered pilot training for the hijackers, flights and living expenses over an extended period of training and preparation.

A Reuters calculation has estimated the Paris attacks - which killed mainly young people enjoying a Friday evening out at bars, restaurants, the Stade de France sports stadium and the Bataclan concert venue - could have cost less around 2 per cent of that.

The most sophisticated part of the attack, making the suicide vests, would have used some of the cheapest materials. Security sources said it would have fallen to an experienced bomb-maker who was likely not to have been one of the actual attackers.

All seven dead assailants in Paris were wearing and used suicide belts, with identical TATP detonation compound, a battery and a blow-up button, French police said.

TATP - or "Mother of Satan" as it is known in security circles - can be made from basic household products and was used in the attacks on London in July 2005 and by "shoe-bomber" Richard Reid who tried to blow up an airliner in December 2001, for example.

The chemical ingredients are available at pharmacies for as little as €5-10 for each belt, and the bolts used in the belts of the three Stade de France attackers would have cost about €150 for 500 bolts each in a DIY store.

There were at least eight attackers and their two Paris apartments - one rented for one week and the other for three nights - could have come to around €680.

The Volkswagen Polo, Seat Leon and Renault Clio cars that investigators say were rented to bring the militants from Brussels to Paris would have cost €595, assuming they were rented for one week, including petrol and tolls.

Finally, a Kalashnikov can be acquired in the European Union for between €300 and €700, the European Police Office Europol says, and the price for 7.62 calibre bullets - the calibre of most of the several hundred bullet shells found outside the restaurants last Friday night - is around €500 for 2,000 on the Internet.

With three Kalashnikovs used in the Bataclan attack and three found in one of the cars, plus probably one other, that cost would come to €5,400.

One of the many costs that cannot yet be reliably calculated, and so not included in the total, is for any accomplices who may have come from outside France and Belgium, with details of the planning and preparations for the attacks still emerging.

For example, one of the suicide bombers at the Stade de France may have travelled on a Syrian passport under the name Ahmad Al Mohammad along a well-worn path of refugees fleeing to Europe through Greek islands.

Estimates of the cost of such a trip from the Syria-Turkey border through Greece - also not included in the Reuters calculations - vary widely.

Pulling together information from travel resources, police and a source at a voluntary relief organisation operating on the island of Leros, travelling from Turkey to the Macedonian border could start at €1,200 - the cheapest option, with no forged documents and using the kind of unsafe dinghies that have resulted in scores of refugee deaths.

This would rise to around €5,000, on a safer boat for the sea crossing and with forged documents.