There are certainly "grades" of fleece, as far as quality goes, but my experience is that 80% of the pricetag is for the name. I have a $400 North Face goretex jacket & fleece combo (when they first came out-likely cheaper now), that has served me extremely well. The fleece jacket has deployed with me all over the place, and is a little worse for wear, but still serviceable. The pile has flattened somewhat-but, oddly enough, still insulates extremely well when covered with something windproof.
I have since gone to a lighter weight fleece pullover I got for $10 at a chain store-which I have had for 2 years, and it has been worn for 2 New England winters (with a windproof layer), and I have been fine. Even if I have to replace it every 3 years (no signs of wear yet), thats still a bargain. I take it camping, hiking, and geocaching, so it gets regular use. Being a lighter garment, it is more flexible than my TNF 300 weight fleece jacket-which now sits forlorn on a hanger. To me, thats valuable in & of itself.
I read somewhere that Malden Mills produces something like 80% of fleece garments made. So, chances are, whether its a brand name, or a cheap one, its made by the same folks.
As for undergarments-when I where long underwear, I usually go with thin silk ones, then polypro over that, if needed. I have a pair of fleece pants I used to use when winter camping, for lounging around-as I dont really do that anymore, they have no use. Yes, polypro gets smelly-but, my only experience, as pointed out by others above, is that, at that point, I smell, so does everything else-as for odor retention, I never really noticed-but, being outdoors, I didnt really care either.