I would suggest an LDO Linear current regulator.
A wizard gets you about 65-75% efficiency. Making some assumptions here:
500mA current,
Vf=3.5V
So using a wizard, input = 4.5V, output = 3.5V, current = 500mA, You will be drawing 555mA from the batteries (if it were in buck mode). So it looks like you actually start out in direct drive or boost mode.
Given the same conditions, with a linear regulator, it'll draw 500mA at the start. So it looks like a wizard would be worse than an LDO Linear.
The linear will start out at 77% efficiency, increasing to 97% when it drops out of regulation.
There are several linear regulator designs that give you less than 0.1V of dropout, meaning you get flat output until the battery voltage drops to 0.1V above the Vf of the LED. At that point, current starts to gradually diminish as the battery voltage drops.
This gives you nice flat output for the majority of battery life, and gives you a nice amount of usable dimming light as the batteries die.
3 Alkaline AAAs can only deliver 500mA for about 20 minutes before they drop down to less than 3.6V. So regulated runtime will depend on current, and Vf of the LED.
Given all of this, your best bet (cost wise) may be to simply use a resistor. 1 ohm should do it.