actually, all of the pres he mentioned cost a lot more than each pre in a mackie onyx does, considering the additional cost of the rest of the mixer.
That's how I tend to think about it anyway.
And of the cheap ones listed, I still would recommend the mpa gold and focusrite as two that have very different sounds and are very very useful in any level of studio (unless you already have lots of great sounding pres that cover all the bases, obviously). then I'd get into mid level stuff like a grace 101, but that's super super clean, great pre though. also the UA solo or 610 or 110 or whatever those types are called, all interesting, the 610 is warm to muddy but nice (too tubey for some folk). also the pres in the meek strips are very very nice, but the comps can be too colored for some folk, but then you don't have to use the comp on everything, the pre alone is nice (love the pre in the sixq, think that's the one with the switchable input solid core transformer on it (iron switch)). then into high end your API, neve, etc., nothing high end will be obviously better than anything good at any cheaper level at first, but when you start mixing you'll notice high end pres are so much better at staying put in the mix, keeping that sparkle, and magical in so many ways.
end of my summary about preamps, all I have to offer in 500 words or less LoL. probably completely opposite to some other people's ideas here though.
Cheers,
Don