Welcome to the LPF. The least expensive ones can be found on eBay. Look for either 301 or 303 style 532nm pointers. They run on a single 18650 battery with the polarity + toward the tail cap. That is because they are Diode Pumped Solid State lasers and the 808nm pump diode is case positive. Good luck.
I have several of these. They tend to run about 80 mW, but can come in lower. I have one doing 50 mW.
The dpss 532's are nice and cheap but prone to heat fade and sometimes mode hop, I really like the 505nm and 520nm directs, you can make your own or buy one online and I really like the deep emerald green 505nm but most of all when pointing towards the sky we have to be very careful to be certain that no aircraft are in the air, I always look and listen for a minute or more and make sure there are no aircraft coming over the horizon especially if you have a tall stand of trees nearby where the view of an approaching aircraft can be hidden so listen carefully as well as looking before you lase, it's a very big deal to say the least, also be aware that any laser over 5mw can harm our retinas and most ebay lasers listed as 5mw are actually stronger so don't let children play with a pointer unsupervised.