Is this the 'rainbow' budget iPhone? Plastic case leaks online amid rumours handset will come in FIVE colours Low cost handset expected to be available in five colours Predictions claim it could on sale in October for just over £200 The casing for a rumoured low-cost version of Apple's iPhone has been leaked online. The technology giant is believed to be already building the new handset, which has a plastic case to make it easier to produce. The handset is expected to be launched in October, and experts predicted it will cost just over £200. Is this the budget iPhone? The rear casing of a supposed cheaper model has been leaked online by website Tactus Apple's current iPhone 5 has an aluminium body, and is only available in black and white versions 'It's been whispered about for a while now, but the above image allegedly shows the never before seen, rear shell of the rumoured budget iPhone,' says the site tactus.com, which does not reveal where the image came from. 'It's also rumoured it will have a 3.5 inch retina screen, much like the 4S, but not as big as the iPhone 5 - a few more pennies saved with that compromise,' the site claims. It also believes the device will be available in Black, White, Blue, Red and Yellow - and predicts a budget iPhone going on sale October 15th for $300 or £229-£249. Earlier this year Apple CEO Tim Cook let slip during a rare interview that an affordable iPhone might be in development. 'We are making moves to make things more affordable,' he said at the Goldman Sachs technology and internet conference in San Francisco. The revelation came after Mr Cook said that he saw a 'wide open field' because Apple's iPhone was currently 'only available to 50 per cent of [mobile phone] subscribers in the world'. Asked whether the problem might be that only 50 per cent could afford an iPhone, Mr Cook said: Good question. Our North Star is 'great products' - we would never do something that isn't a great product, that's not why we're on this earth. 'That said, if you look at what we've done to appeal to people that are price sensitive - lower price of iPhone 4, iPhone 4S, in most recent quarter, not enough supply of iPhone 4 - surprised us.' Tim Cook, Apple CEO (L) and Dave Grohl of the Foo Fighters look at the new iPhone 5: The firm is now believed to be developing a cheaper, plastic version to go on sale later this year The leak comes a day after it emerged a loose-lipped supplier who hinted that Apple were slowing down production of iPads and iPhones wiped $22billion off the company's market value. Shares fell below $400 for the first time in a year and a half, following the comments from audio chip supplier Cirrus Logic. The decline means Apple has lost its position as the world's most valuable publicly traded company to Exxon Mobil, which has a market capitalisation a few billion dollars above Apple's $380 billion price tag. Apple Inc shares briefly fell below $400 April 17, 2013, the first time below that level since December 2011, leading a broad selloff in U.S. equity markets. On Tuesday, Cirrus Logic, which supplies audio chips for the iPhone and iPad, said sales of a particular chip are slowing down as an unnamed customer moves to a newer component. Cirrus did not name the customer, but Apple accounted for over 90 percent of its business in the December quarter.