There are a few things to consider when purchasing an air rifle under $150. The most important factor is the purpose of the gun. If you plan on using it for hunting, then you'll want to make sure it's powerful enough to take down game. If you're only going to be shooting targets, then power isn't as much of a concern. Other factors include the type of action (single-shot or repeater), caliber (.177 or .22), and muzzle velocity. Weighing all of these factors will help you choose the best air rifle under $150 for your needs.