In my sidebar I recommend using an old abandoned computer to learn the LAMP stack. If you, friends, or family, have such a computer sitting around, it's obviously the cheapest path.
The Raspberry Pi is a very similar and low cost alternative. As Roy Wood reports:
The Raspberry Pi system is a single-board computer based on the Broadcom BCM2835 system-on-a-chip. The specs include a 700MHZ ARM CPU, a VideoCore IV GPU, up to 256MB of RAM, an SD card reader, USB ports, and an optional ethernet port. The device supports common USB peripherals like mice and keyboards, can be connected to a TV or monitor, and will run Debian Linux. Oh — and did I mention that a Pi will cost a mere $25 or $35, depending on the model?
The Pi is just entering production. It is an alternative, but might be a little tight on memory, compared to the typical disused closet PC.