I'd personally save up some money and get yourself a good one. It's a great investment, and after using a cheaper one for awhile you might resent getting it in the first place. Things to look for, so you don't feel shorted.
I'm currently using a Wacom Intuos 3:
Pressure sensitive
Tilt sensing
The ability for it to behave like a pen in the bounds of it's screen, instead of like a mouse (What I mean by that is if you place the pen in the upper right part of it's area, you want the cursor to instantly be in that area of the screen,... hard to explain)
Buttons on the pen (I keep mine "undo" and "right click") so your hands don't have to leave the pen
Eraser on the reverse side. (I've gotten horribly used to this, but hated it at first)
Buttons on the tablet itself (mapped mine to "delete" "save" "test movie" and a few others.
Just getting on that "feels" like you're holding a pen, will be a letdown. I'm not sure of the inexpensive options out there.