Cost effective way to protect circuit from overvoltage
Probably the most common method is to use a fuse with any (and sometimes all) of the following: -

A regular power zener diode
A power shunt regulator (like a zener but programmable)
A crow-bar circuit (on over-voltage, it clamps to close to 0 volts)

So, if the voltage exceeds a certain level, too much current will flow into the aforementioned devices/circuits and then the fuse blows.
You can use resettable fuses too (polyfuses they are sometimes called). Once power is removed, the polyfuse resets.
An alternative is a series-connected over-voltage circuit that &quot;disconnects&quot; when the input voltage exceeds a certain critical level. Not too tricky to design but, they should also be used in conjunction with a zener to ensure that fast voltage rising events are dealt with effectively.