We have made the best experiences with Wacom tablets. Usually we go for the Intuos series. We've been using Intuos2, Intuos3 and Intuos4 tablets with good results. So if you wanna save money, it's definitely ok to buy an older, used Intuos tablet.
The major advantage of Wacom tablets, apart from their excellent build quality, is that they don't need batteries in the pen (“Penabled” technology).
There are many cheaper tablets on the market (e.g. Genius) - here the important thing is to make sure that they are using the WinTab driver, which is a windows driver provided by the tablet manufacturers to communicate between the digitizing tablet and Windows programs. Tablets that don't support WinTab won't be recognized by the Nodekit. Many people owning the low-end Genius tablets have reported that they don't work with the Nodekit.