[Pokiehat]

If you don't use a preamp with your NT1, the signal going into your soundcard's mixer will be tiny so you will end up having to pile on about 40 to 60dB of gain post recording which will sound awful and hissy.

Other than that, how cheap is cheap? Preamps are one of those things you can spend like a 100 bucks or several thousand bucks on.

In order of cheapness...

M-Audio Audio Buddy. Its pretty good and you wont find anything better for less money. Supplies phantom power if you need it and it has instrument level inputs so you can run a guitar pickup into the front.

Focusrite Green. If you can find a Green 1 or something for significantly less than an RNP or a Brick then its a good deal. Otherwise avoid. Don't ebay them since they were notorious for having crappy pots and switches. Heh, also a hot contender for ugliest rackable gear award.

FMR RNP. The compressor (RNC) is kickass. I think the pre (RNP) is a bit overrated but its popular and definitely fills a gap in the market (there is a dearth of 2 channel pres for under 500 bucks). Gain steps in 6 dB increments for reasons I have no idea why. I personally think it sounds exactly like my onboard pres except the gain trim jumps in massive steps. If you already have something like a Saffire, Impact Twin or Fireface as your soundcard you don't need this.

The Brick. It kind of looks like a brick too. Only 1 channel this time but it'll take anything, even a guitar pickup since it has a built in DI to switch down the impedance. It ain't exactly quiet but its really nice.

Focusrite ISA one. It looks like they are selling these for less than 500 bucks now which is kind of an insane price. I always liked the 'blue' preamps. Some people say Focusrite pres are boring but whatever. You only get 1 channel but its a good channel. Careful. It gets hot enough to cook eggs on it.

After that it all gets very expensive...