What do you do with dead hard disks? I usually salvage the magnets; the larger ones make perfect holders for things like tools, knifes or mobiles.
Here's my ghetto mobile mount, mk.2: a 3x3cm piece of thin sheet metal sellotaped to the back of the phone and two fat ex-disk magnets screwed to the dashboard. Plenty strong, vibration-proof and completely invisible under the silicone phone cover. And, of course, zero cost.