I'm looking for an old PC in working condition.  Doesn't need to be flash or fast - just a complete system (no monitor, if it has HDMI output).

It's a project for my two kids - 8 and 5 - over the school holidays.  My idea is to teach them about computers - the different components, how they work, and how to disassemble/re-assemble a PC.  So I'd like to find an old PC which has no useable value, but which is still in working condition with the major components - motherboard, RAM, CPU, PSU, graphics card, storage - so we can put it all back together again and they can see that it works.

Preferably free and local (Palmerston North), but happy to pay a small amount if necessary.  We likely won't be using the PC at the end for any actual games or programs, so would ideally suit a PC that is destined for e-waste recycling.