This has been reduced recently down to £10. Purchased 2 of these for our cars and they work a treat. Very solid unlike the cheap plastic versions. They come with 2 metal plates.
1. To stick on your case
2. Large plate to insert between smartphone & case
Now both our phones just magnetically connect, instead of mucking around with the sliders on my previous cradles.
Nice solution. They also sell silicon cases with the metal already built in