The best money I've spent on professional development is paying to travel to industry conferences at which I was accepted to speak. Like many people, I was ner

The best money I've spent on professional development is paying to travel to industry conferences at which I was accepted to speak. Like many people, I was nervous about public speaking earlier in my career. Out of a desire to improve myself and to "give back" to the community, I applied to speak at some industry conferences. Many people think about conferences as TED-talk style luxury events, at which speakers are compensated for their time and expertise. In reality, the only thing most conferences give speakers are a few free tickets to the conference and access to speaker-only events. Travel (and often lodging) need to be bought out-of-pocket. By putting myself out of my comfort zone and speaking at these conferences, I developed valuable skills that significantly helped my career as it continued to develop. Being able to speak confidently in stressful situations -- to a wide variety of audiences -- is a very valuable skill to have. In addition to the confidence boost of getting some talks under my belt -- and the actual skill of public speaking -- the networking opportunities afforded to conference speakers are often unmatched. I was able to have intimate conversations with leaders in my field (information security), and learn first-hand how luminaries think about contemporary challenges. I realize this answer probably doesn't conform to the type of response that OP was seeking, but it's the truth of my experience. Good luck!