To get exactly what you want, it would likely need to be built specially for you. That means it would be more expensive than most. However, if you can live with one that outputs about 50 mW, look on eBay for 635nm or 638nm laser pointers. They normally run on two AAA batteries and can be had for $5.00 or less. I have one or two in my collection. They are black coated pens with a tactile switch on the side.