What is the cheapest/smallest mac?

The contenders I can think of are;

Quadra 700

Powerbook duo 280c

MacMini

I want something... I think I could live with os 7.1 if I needed to, but os 8.1 is better....

I'm not keen on os 9, but am keen to try os 10

I need to transfer files and could do with the mac being fairly portable...