9x12 is a very VERY large size for a tablet, especially if you've never used one before. Those are best in smaller sizes because they're easy to handle. You'll end up zooming in and out on your pictures anyway, and drawing on a tablet works differently than drawing on paper. Just imagine if you had to move your mouse around that length to use your computer. I dunno about you, but that's sorta cumbersome.
You'll be looking at the screen when you draw, so having less of an area to fumble around with is a good thing, even if you don't normally draw small pictures. I'm used to drawing on 8"x11" paper, but drawing on a tablet even a bit more than half of that size is cumbersome and annoying. Also, have you considered where you'll store this tablet? A 9x12 sheet of paper is a very different beast than a 9x12 hunk of plastic and wires.
As for saving money, this is a difficult thing with tablets. I reccomend you don't buy tablets from anyone but Wacom- they're the most reliable tablets on the market. Sure, they're expensive, but you won't have random issues popping up that can't be fixed by a quick software update like
King Moogle had earlier today.
Like Lene said, 4x5 Graphire, usually retailing for $99, is the best way to go for that budget. Don't buy random no-name tablets for pricing without doing a crapload of research first.
