I tried a few cheap cables (lightning and iP 4) from eBay – between £2 and £7 – and they all failed in one way or another. Cheaper ones usually fail from the plug falling apart, pricier ones from cable collapse. It started to feel like false economy, so I’m currently using an Apple lightning cable – four months old and doing fine.
I should add that if it were only home use, the cheaper cables would probably be perfectly adequate. It’s in the car, when it gets dragged around a bit, where the premium cable seems like the better bet. Other people’s experience may differ entirely.