What a difference a year makes. The last time Unrefinery looked at loafer socks the cheap ones were relatively crude and the good ones were $15 a pair. Nowadays the options are plentiful and inexpensive. Three options for your consideration:
Timberland Men's Boat Shoe Liner No Show [$5/pair] — The best reviewed here, with the lowest rise, medium weight and comfortable construction. Timberland. Go figure. Buy these if you only buy one kind.
Thirty48 No Show Loafer Socks [$3.50/pair] — A tough, durable-feeling knit with a silicon grip pad to hold them in place. Best variety of colours. But also the highest rise, and thus wearable with the fewest loafer styles.
Fruit of the Loom Men's Extreme No Show [$1/pair] — You don't expect a lot for a dollar but these have a mid-height rise and were particularly comfortable due to their breathable mesh construction. At this rather disposable price, durability would be a bonus, so worth having a pack on standby.