Thanks very much for the advice guys - I really appreciate it. I will go with a condenser mic and an interface then. I was also thinking about buying the Rode NT1A Mic and the Audient ID4 interface but the latter has only one mic input (like the Focusrite Solo) and the more expensive ID14 (which has two mic inputs) pushes everything out of my budget. The Focusrite 2i2 package is definitely within my budget but I've read mixed reviews about it with some people complaining of a hissing sound and other glitches. Do you have experience of using it?
From what I've read here, the NT1 (sans "a") gets slightly more nods in that price range.
When you sell a crapload of something, as Focusrite seems to, there's always going to be unhappy folks. I'm a F'rite user, though an older Saffire model, but it's been fine on my Macs.
"Hissing" usually means the gain is turned up quite a bit, and that can be a problem with these if you use a low sensitivity dynamic mic, which many folks are trying to do by pairing up the Shure SM7b and 2i2, apparently. (Even a Shure SM57 is going to have you pushing the gain knob.) Anyway, there are a lot of interfaces in that class - I'd go to your favorite re/e-tailer and read reviews. Personally, I think that's a commodity market and by and large you get what you pay for, though in some instances, a some of what you are paying for is a big marketing department
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And here's the first learning curve bit - you don't have to get the recorded track pushed all the way to see the waveform bumping up against 0dB like in the old tape deck VU meter days. The downside of 24-bit recording and low noise floor is that it can be hard to hear yourself in the headphone monitoring when tracking, so folks dial up the interface GAIN knob, adding unnecessary noise, ambient sounds, etc., when what they should do is change the master fader in the DAW, or perhaps spend $80 (or so) on a headphone preamp.
If you don't have good tracking (closed back, reasonably "flat") headphones, you should include those in your list.