the arduino nano is around $3, all the other components are drawer junks. even if you buy one opamp, some resistors, one speaker I doubt it will cost a lot more than $10. the box is optionnal and should cost me some $4
hmmm I don't know a lot about arduino though I have done some projects with Arduino Uno and a 32bit 3.3V Arduino I don't quite recall the model so I learned some stuff about programming them
Anyway the schematic says Trinket Pro which I don't have. I don't have the buzzer, the MCP6041 or the MCP73831. All the other components I have
So just looking at ebay for current UK prices inc postage (I buy my components when I briefly return to the UK every 6-8 weeks)
Trinket Pro...... £12.50
MCP6041........ £2.20 (8 pin DIL)
MCP73831.......£1.98 (or I buy 20 from china for £1.50 and wait a few weeks
LD-BZEN-1205 £4.92 (for a pack of six. Cant see a UK supplier sells them individually
Trinket Li/Lion backpack is £7.50 and then I don't need the MCP73831 so add £5 to do it that way. And I still need to get the battery
So that's about £20 to build (approx $26) or £25 using the backpack - and I get some spare Buzzers and maybe Op amps to go in my component stock. I'm not saying that's expensive for s useful toy
but it ain't $10
Rich