Bulb is cheap... but you need a green one, or a green condom to fit over it. Otherwise you'll have white light (or whatever color you put in).
You can also put some LEDs in there and make it way cooler. If you want to keep the stock green, throw some green LEDs in there and never worry about them going out again.
How to for the LEDs
BTW, it's a #74 wedge base IIRC. Looks just like a 194 bulb (you know, like the footwell lamps), but A LOT smaller.