Liger Electronics via Amazon offers the Liger Magnetic Air Vent Mount for Smartphones for $9.95. Coupon code "UHB5N9JU" cuts it to $6.95. Plus, Prime members receive free shipping. (Non-members can spend $35 or more to qualify for free shipping; otherwise, shipping costs $6.07.) That's $3 off and the best price we could find. It uses a rubber clip to attach to your car's air vent, then magnetically holds your smartphone in place.
Hisgadget Inc via Amazon offers Prime members a similar items for about the same price via coupon code "Q34ALUSM".