PaulS:
Blimey thats a bit more of a circuit than I imagined for this type of thing!
Its two resistors, two diodes, and a capacitor. In bulk, you're looking at 10 cents a sensor.
What I meant was rather than just a single wire connecting straight into the board and being able to be read as resistance to earth you ad 5 components per sensor, so if I used all the analogue ports, theres 25 extra components to get just 5 sensors to work and if I started multiplexing for more sensors suddenly its a world full of components just to get a few readings.
From someone who is new to more complex electronics, you soon realise how some things can have such large amounts of components in to even do a simple job!