Applying power to a circuit only when a certain input voltage has been reached
Expanding on your idea here is something that might work:







simulate this circuit &ndash; Schematic created using CircuitLab

You should choose R1 and R2 so that their sum is less than \$17k\Omega\$, but their ratio can be pretty much anything: the constraing on the mosfet maximum gate source voltage is (quite) relaxed. You can possibly even use a relay to dissipate even less power, but you need to be sure its coil can be powered through R1.