"Once you require two mics, you obviously need a mixer of some sort"

Not necessarily at all - I've always used 'breakout box' soundcard interfaces. I've never owned a mixer and never intend to. More commonly known as USB soundcards or Firewire soundcards. I now have a Mark Of The Unicorn interface, on which I could be recording 5 instruments at once, and I still wouldn't need a mixer. That's what the software's for (among millions of other things).

There are plenty of affordable ones with two inputs. (More than two inputs and you're looking at upwards of £350)

In fact, I'll be selling my M-Audio Firewire 4010 shortly on eBay. I'd keep it, only I recently bought a new MacBook and hadn't noticed that they've removed Firewire from it. I was mighty pissed off, and bought a USB one instead. That did me proud though - two inputs on the front double as XLR or 1/4inch jack, and a firewire cable goes straight into yr computer. The pre-amps on it are noiseless, which is more than i can say for any hardware pre-amp under £200 that I've ever tried.

To be honest, that's the package I'd recommend to anyone starting out from scratch who wanted to make pro(ish) recordings: a USB or Firewire soundcard; a decent condenser mic.

And eventually a pair of good monitors (but I don't see much point until you're ready to properly release and promote an album).