There will be those who say cheap cashmere is a false economy. However, I have a beautiful Tesco cashmere jumper which looks good as new despite being 5 years old now. My Jaeger version shrank & bobbled horrendously within a couple of wears so I don't think expensive always equates to quality.
I think it's hard to know how it will go. I have a h and m 100% cashmere cardigan and that is still going strong 3 years later if that helps, and it is super soft. I have had some cashmere from tesco - some of it bobbled, some didn't - likewise some marks and spencer jumpers have been of different standards, so it is hard to predict how it will go even when buying from the same brand.
I have cheap and expensive cashmere. It all bobbles, some even shrink regardless following strict instructions. My la redoute turned out to be better quality an fit than my YMC stuff, which cost close to £200. You live and learn.
They say turning inside-out prior to handwashing reduces bobbling. And get a cashmere comb!