We’ve featured a plotting machine kit before, but if you want something that’s ready to go out of the box then check out the AxiDraw, a USB plug-and-play machine by Dr. Lindsay Wilson and Evil Mad Scientist.
AxiDraw can write or draw on practically any flat surface using normal writing implements, such as a ballpoint pen, chalk or an edible marker. It can hold implements vertically or at a 45º angle. It covers up to an A4 paper, but you’re free touse it on surfaces that are larger than that. Using a vector graphics application such as Inkscape, you can use it to mimic handwriting, decorate food, make posters and much more. You can watch a demo of the machine on its product page.
You can order the AxiDraw from Evil Mad Scientist for $450 (USD). It’s definitely not cheap, but considering you can run a small business with a couple of these I think it’s priced just right.