If you don’t have an agent, and you’re just starting out, you’ve probably heard from other actors that if you spend money on headshots, once you get an agent, your agent is going to ask you to re-shoot. That's not true. The reason most agents ask actors to reshoot their headshots is because they got cheap ones in the first place! In the end having to shoot twice, rather than shooting once and spending the money then, ends up costing you more.
Regardless of how expensive or cheap a headshot is, you still have to spend the money reproducing them and distributing them. So why spend that money twice? If you do it right the first time, not only will it cost you less in the long run, but any legitimate agent is going to recognize your headshots to be high quality and not ask you to reshoot. It also means you’re invested in your craft which in turn means you’ll be taken more seriously.
Professional headshots should not only score you great representation, but they should also bring back a return on your investment for years to come. After that, the only reason to reshoot would be if your look has drastically changed.