Liquidware (an open-source electronics firm) has released a kit that can be used to make a linux tablet with a 4.4″ (480×272) OLED touch display.
The kit includes a BeagelBoard Rev C4 board (with a 720Mhz ARM Cortex-A8 OMAP cCPU, 20mm speaker, SD slot (it comes with a 4GB card), Wi-Fi, mini USB port and a battery.
So you won’t get a real tablet – it’s very thick, and not very pretty – but you can play videos and access the web. And it costs just $393. Here’s a short video on the kit: