Getting your airman ratings can be one the most expensive endeavors you ever set out on, whether for a career or a hobby. However, there are a few certificates out there that are relatively inexpensive to obtain compared to a PPL or Commercial Cert, and can helps open up other doors in aviation as well as make you a better and more knowledgeable pilot.
Advanced Ground Instructor (AGI)
What you can do with an Advanced Ground Instructor Certificate:
Instrument Ground Instructor (IGI)
What you can do with an Instrument Ground Instructor Certificate:
If you already hold a valid pilot certificate
If you do not currently hold a valid pilot certificate:
What can you do with a sUAS certificate: