“The Raspberry Pi is cheap.”
The RRP for a Raspberry Pi model B is £36. And yes, at a tenth of the cost of an iPad it’s within the range of most families, teenagers with a Saturday job and indeed schools. However, your £36 doesn’t get you a fully functioning, ready to program Pi. You need a few other bits and pieces if you want to do more than merely admire the circuitry. Unlike the iPad or indeed a laptop, Pis do not come with a fully integrated power supply, or a screen, or a keyboard, or a mouse. Not even a case! Without these things your Pi is just a circuit board. And these things will cost more than the Pi its-self.