I'm on the "drew the short straw" on the sweat scale, so for me, the warmth of the base layer isn't as much of an advantage. I get cold like anybody else, but the point is I don't want to spend $60-$90 or more on something like that when I know by the end of any given day, if it's remotely "non toxic", I wasn't working hard enough!
I like lightweight, inexpensive base layers that I can buy enough of to change every day. Even backpacking where I re-wear a lot of stuff, I always have a fresh base layer and pair of socks for every day of a trip. For cold days I've had really good luck with the 32 Degrees thermal underwear Costco sells. For moderate days a lightweight undershirt like you'd wear with a suit works great. For warm/hot days I love Patagonia's "Capilene" shirts. Those days are the only days I wear anything expensive because I've also found Sitka's Hunting Core Long Sleeve Tee is about the same in terms of keeping me cool and dry (and providing both camo and UV protection at the same time).
To be honest I'm pretty mixed on my outer layers as well. Given how much attention they get (and sponsorship they throw around) I invested in some additional Sitka layers, but I haven't been too happy with them. For as much as they charge I expected their stuff to be quieter. I've gotten random-brand base and outer layers from McGuckin's on seaon-end sales that outperformed some pretty expensive gear.