The founder of the One Laptop Per Child (OLPC) project, which aims to deliver $100 laptops to schoolchildren in the developing world, has said that the machine will now cost $175 and may not start production until October.

Nicholas Negroponte, the former director of the Massachusetts Institute of Technology Media Lab who heads the not-for-profit project, said that it was now "at the most critical stage of its life," but remained optimistic about its prospects, adding that new countries, including Peru and Russia, had inquired about taking part.

The rising cost of materials – in particular nickel – is responsible for the increased price of the machine, an OLPC spokesman told TimesOnline, while the roll-out had been pushed back because of changes in the design, which were "not unusual in technology development projects."

At least seven countries – Uruguay, Nigeria, Pakistan, Argentina, Brazil, Thailand, and Libya – have expressed interest in buying the green and white machines, which have a crank so that they can be wound up by hand, but the project requires orders for three million machines in order for manufacturing and distribution to begin.

Mr Negroponte said that the computer, which has indoor and outdoor reading modes, will now be able to run Windows in addition to its own open-source operating system, which was developed with the help of Red Hat, one of its sponsors.

Despite the price rise to $175 (£87), the laptop remains dramatically cheaper than most models, largely because it uses very little proprietary software. Quanta Computer, the Taiwanese manufacturer which will assemble the machine, had agreed to take a profit of about $3 (£1.50) per laptop – less than what it takes from other PC makers, Mr Negroponte said.

The project had also been working with developers at Microsoft so that the computer could run a low-cost version of Windows, which may be the $3 'Innovation Suite' announced by Bill Gates in China last week for governments that subsidise student computers.

OLPC's organisers have always maintained that $100 was a long-term target, and that they expect the cost of the laptop to drop by 25 per cent per year over the life of the project.

Mr Negroponte also said that the project was considering shipping the machines to poorer schools in the US.

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