Cheap, decent, thin synthetic socks?

Defeet aireators, typically available in a 3-pack.

WrightSock coolmesh are my personal favorite. Double layer but still thin and dry quickly.

Anything that goes up about 8" on the leg?

Wigwam Gobi – all polypro, very durable, very thin, dry extremely fast.

n/t

+2 on WrightSock coolmesh. The double layer is awesome.

In my experience most of the thin poly socks don't last very long, and that includes DeFeet. What does seem to last is Pearl Izumi Attack Socks, which is interesting since I suppose they're designed for cycling. Usually I find them for $8/pr at REI, which seems reasonable to me given the superior durability.

http://www.campmor.com/Product___90050

I have some of these that are almost 20 years old and still going strong despite looking quite funky… used in the winter with Thorlo wool/spandex blend, also indestructible. But I have some Darn Toughs that I haven't even worn yet.

But for use with trail running shoes (Brooks Cascadia) the Wright socks are best for me.

YMMV, HYOH and all the usual pc acronyms…