The one I bought is the cheapest one they make. It's still extremely good for it's size and price. This drawing I made with it (just a week or so ago) made it on EqD twice, so don't doubt its possibilities, because most limitations it provides are not by it's size, but by drawing ability. If you have the ability to go beyond what it allows you, you would still be able to draw amazing stuff with it and save up to buy a better one.
I'm currently actually saving up to buy a Wacom Cintiq 21 IX ($2000) but that's a while away and I'm doing it to move up to Photoshop.
I would use Photoshop if I had a tablet that had a display on it, but all of those are over $1,500 so I doubt you're willing to put that much money into it. Paint tool SAI is ideal because it has a line smoothing feature. If you can't see the display, your lines tend to be a bit bumpy, but that can be adjusted by Paint Tool SAI. You can also draw with vectors which allow you to be able to edit lines in the drawing. Photoshop on the other hand is much more powerful and has more capabilities, but its lack of a smoothing feature prevents so many possibilities.