Rowan Linen Drape
55% linen, 45% viscose, comes in 50g balls costing about £3.50.
It's gorgeous, drapes really nicely. After washing, my swatch was a little stiff, but after it dried it was fine again.
This yarn is an absolute pig to crochet with. It's made of nine separate strands which just love coming apart, and it's hard to get your hook into the right gap without watching it carefully. It's much, much easier to knit. Knitting also shows off the drape better than crochet.
Unfortunately linen drape has been discontinued by Rowan.