They range in price from $100 for discontinued cheap ones to $500 for more powerful ones that can pick out a flag at 500 yards. I have a Bushnell 1000 which will reach a helicopter at less than 1000 yards, and any flag you can see on the golf course. As far as veriflying your flight altitude, not sure if you mean from a real plane to the ground, or from you on the ground to your bird directly above you. The former for sure, and the latter certainly to 500 feet!
The target size and color determines the reflectivity, with darker colors slightly harder to pick up. Mine also has a 6x magnification to make placing the beam over the target easier. Cost about $400 over 5 years ago. Powered by a 9v battery.