Hi
A simple Zener diode voltage regulator might do the trick. I punched the maximum values you mentioned into this online calculator and it appears a 14 Ohm resistor (so you'd use a 15R) along with the 3.6V Zener diode will cover it off nicely. A very cheap solution too.
I'm not certain what will happen inside the 2V headroom they suggest for the voltage, so need to do more reading. If that's a problem perhaps a potential divider with just two resistors will be more stable?
Cheers ! Geoff