Cheap 12V to 5V DC-DC converter for PCB?
A buck converter is the classic way to do this. It requires input and output caps, an inductor, a controller chip and optionally (depending on the controller chip - some have synchronous rectifiers built-in) a Schottky diode.

I am a surface-mount guy, so I don't have a particular part to recommend for through-hole. I use the AP1509 pretty routinely for this job.

Buck converters are preferable to 7805 style regulators because they're much more efficient. Rather than dropping the voltage with resistance (dissipating the voltage drop power as heat), they directly convert wattage at one voltage to the same wattage at a lower voltage (at 80-95% efficiency, generally).







simulate this circuit &ndash; Schematic created using CircuitLab

Here, the "switch" represents the buck controller (not shown is the feedback from the output to control the switch frequency and/or duty cycle). The switch closes to charge the inductor, raising the output voltage. Once the output voltage is high enough, the switch turns off. The inductor will develop a voltage across itself as the coil collapses. The Schottky diode will anchor the left side to ground, forcing it to power the output. Eventually the output voltage will fall, and the switch will close, and the cycle will continue.