Hackable Hardware?

Cédric Adjih asks: "I wanted to build my own small-and-cool RISC box (such as an Itsy), or even much smaller, in order to control self-made robots, or other simple homebrew electronic circuits. But the retail-price for individual electronic components is often way too high ($1000 for a RISC evaluation board, $150 for a RISC processor, $1000 for PC/104 with 486 card, ...). Since there is a trend towards more and more powerful and cheap electronic devices (calculators, PDA, agendas, Inet boxes,...), the only rational way is to buy one, and to hack it. But this require internal hardware information, and also a way to interface with circuits (such as via I2C). Does anyone have information about WWW pages describing such hardware or such hacking? An example candidate for the low-end would be the TI-89 (68000 at 10Mhz, 188K ram, 384 K Flash, easy interface with PC, LCD display ; at $150+. Hard to beat that by buying the individual components...), but there might be better, or more powerful... "