I know almost nothing about electronics, but I've been looking in to the Arduino project and came across a super cheap (albeit self-made) alternative called "The Shrimp" - which, I figure, would be a much cheaper solution when deploying your invention rather than using an actual Arduino (though you'll need to add some extra parts depending what functionality you require).

The official page says that it "costs just £1.40 in components when bought in volume" (about 20 ZAR) - excluding a USB connector, which technically isn't after programming (so it can be re-used). I've attempted to find local (South African) prices for all the parts, and hopefully I've matched everything up correctly:

• 1 x ATMEGA328-PU @ R40 each
• 2 x 22pF Capacitor @ R0.20 each
• 4 x 100nF Capacitor @ R1.65 each
• 1 × 10µF Capacitor @ R0.58 each
• 1 x 10KO Resistor @ R0.15 each
• 1 x 1N4148 Diode @ R0.22 each
• 1 x 16MHz Quartz Crystal @ R4.31 each
• 1 x 6mm Tactile Switch @ R2.15 each
• 1 x stripboard @ R7.25 each

(Note: some items come in a 5 or 10 pack, and the stripboard should make 3 circuits)

Total: R67.50

That's still excluding the USB interface, which I'm yet to source... apparently Nu Vision Electronics sells (and delivers) them locally. Despite the great "international" prices, it works out way more expensive after shipping (eg: http://za.mouser.com/ want R600 to ship an ATMEGA328-PU to South Africa :P)