I think you mean the costs for a new pcb,
since e.g. TI want only 0.71$ for its TPS3824.
It gives you both, a watchdog and a right power on reset.

There is no other way to get well reliability.

Also micros with internal hardware watchdog
gives only less reliability without a proper
power up reset.
E.g. the simple RC reset circuit works only after a
long power off time to discharge the capacitor.

Any software watchdog routine can only work on
software errors.


Peter