Here is the Dilema. Do you want performance, versitility or cheap? I go with performace, and let skill do the versitility bit.
Here are some of the ones I have seen and a couple I have used:
Stanton Final Scratch
Not available these days unless its second hand, I had a Mk1 version, USB connectivity and the Software was only stable on a MAC, even then, a little tempremental!
Recentley borrowed one of these of a mate, and I have to say I was impressed, easy to use, stable, even on Vista! and quick response from the USB hardware.
Native Instruments AUDIO8 DJ
I am itchin to get hold of one of these, it looks pretty impressive and ticks all the boxes in terms of functionality, Firewire interface so it should be spot on for scratchin, and based on the latest version of Tractor FS, so again, proven technology.