How hot does a voltage regulator get?
The heat produced by a voltage regulator isn't a function of the voltage, it's a function of the power.

You can calculate the power the voltage reg will dissipate by taking the voltage-drop across the regulator, times the current flowing through the regulator.

E.G: $$Power = Volts * Amps$$

In other words, if you have a 30V source, and your device is running off 3V, you have \$30V - 3V = 27V\$ across the regulator. However, if your device is only drawing ~3 mA:
$$27V * 0.003A = 0.081W$$

You would only have a dissipation of 81 milli-watts, which wouldn't even get too warm to the touch.

However, if you have a 5V input, with a 3V output (giving 2V across the regulator), yet your deice is drawing 1A, you have:
$$2V * 1A = 2W$$

You have a power dissipation of 2 watts!



Basically, there is more involved in evaluating heat production then just the voltages