What's cheaper than a Raspberry Pi and runs linux well?

I'm interested in playing with some of the new virtualisation technologies, such as docker. For this stuff my usual go to toy, the Raspberry Pi doesn't quite cut it. This morning I spotted a Dell Optiplex PC, Core 2 Duo 2.5GHz, 2G Ram, 250GB disk for $35 on eBay with no bids.

Ending an auction at 7:15am on Sunday morning may not be the best way to sell technology.

So far I've installed the 64bit version of Ubuntu Server 14.04 and following the instructions from the excellent Ubuntu documentation created a virtual machine in which I've installed another copy of the Ubuntu Server.

This works magically, the qemu environment can be set up to share the virtual console via VNC and from my desktop machine I answer the install prompts as if sitting at an actual machine. Here's how it looks:

Now I can safely try all sorts of crazy things in this virtual server and just delete anything I'm not happy with.

Here's the giant new server (with a Raspberry Pi next to it for scale):

There are bargains out there, but I should say that this was a crazy price. You can pick up similar systems for under $200 pretty easily though.