Typically the nominal current for one of these Laser Pointers [and I'm assuming "Red" because of the description of it as a cheap, Dollar Store pointer], is 20ma. If this is the case for your pointer, then there is an IC [looks like a TO92 transistor] designed to drive LEDs at precisely 20ma.
The CL520N3-G!
54¢ at Mouser.
There's also one for 25ma: CL525N3-G
It requires a minimum of 4.75 volts and has a "dropout" voltage of 1V [i.e. it will go as low as 1V when trying to keep the current at 20ma]. Thus, the Max Laser Diode Forward Voltage + 1V = Minimum Power Supply Voltage OR 4.75V -- whichever is larger.
This is a "Current Sink" device, so you will need to insert it at the "negative" side of the Pointer circuit. Check the datasheet for an example of how to use it.