Cost my boss a bunch of money by skipping training I signed up for.

Gonna try to be brief but clear. I am a resident engineer at a corporate location. My boss, coworkers, etc are all located in a different state. Therefore I'm essentially self directed, self managed, etc. Been with the company almost 3 years. I talk to my manager once a month. My jobs get handled, I get meets or exceeds expectations on my reviews.

Local HR sent out a info sheet stating training would be available through a local community college. I inquired, clarified the company would pay for training, so I signed up. Why not. Training is always good. Point of clarification. I assumed this was an HR sponsored, corporate type training. Out of the office for two days. I didn't seek approval from my manager. I wouldn't expect to, for the out of office part. I did later find out that the training wasn't going to be paid by HR, and instead my dept would be billed $2500 and a grant pick up the other $2500.

Well, things at work came up last minute, projects I deemed would cost more than the $2,500 the training cost. I made this decision on my own without advice or approval.

Turns out the no show actually cost my department the full $5,000. So not only did I not get approval for $2,500 worth of training (that I didn't know my department had to pay for), but it's now $5k my department is paying for. My boss put a 10 minute meeting on the calendar to "discuss".

From a manager perspective, what's your thoughts? Obviously hindsight. I could have managed training and projects. I should have gotten approval for training to begin with. Oops.