I meant Chinese clones. Arduino is Open Hardware, it's perfectly legal (that's kind of a point of Open Hardware movement). It's equivalent in form and function to the genuine Arduino made in Italy.
You can get a Pro Mini clone for less than $1.50.
A full-size Arduino R3 clone (with a cheaper USB chip, the CH340G) is less than $3 with free shipping.
But if you are not planning on using shields you can get arduino mini for ~$1.3 or nano for ~$1.8