You can make it yourself if your on a budget.
Taping a magnet to your face won't do anything, thats a stationary magnetic field, not a time varying or moving as its called.
Its not easy to make your own, you have to know your electronics.
I heard the capacitors blow up if you don't have a diode in the circuit.
Anyways, probably some cheepo ones on the net, but remember the cheap ones capacitor will probably blow up on you after using it for a while.