Best cheap way to connect microphone to PC?

My boyfriend is a pretty good singer and I'd like to get him a better microphone. He now has a cheap USB mic. I'm probably getting him a Shure SM58, but it still needs to be connected to his laptop. So far I see 2 options:

1) USB audio-interface with mic input

2) Or I can just build a DIY mic preamp (which would cost me roughly $30) and the output can be connected to the jack audio-in of the laptop

What would be the best sounding way? I wouldn't want the sound quality to be degraded to the level of any USB mic with a crappy audio interface.

Any ideas? Help is greatly appreciated

USB interface because it's more versatile.

B&H has some for like 40-50 bucks.

i have a tascam us122L but there are better ones out there.

I have a US122L too, but the thing is it costs as much as the microphone. Also amplification is very important so I'm not sure if a cheap USB interface will cut it?

well in music equipment, u more or less get what you pay for to a certain extent. u should know that by now.

I recently bought the Se2200a condenser. I know they have a USB version of this mic but it may be above your price range.