I just got a hold of a really nice Groove Tubes GT66, but without a proper interface -- just that power supply and a few cables.

I don't have much of a disposable income, so I was wondering where I could get a decent, cheap ($50-$100), entry-level interface. I was looking at the entry M-Audio and the Lexicon Alpha USB interface. Are either of these good? And if so, is one better than the other?