If the first example differs in that the instructor will facilitate 2 three-hour sessions instead of 1 six-hour session, the cost should be spread across the two sessions.  If we assume that the estimated total cost is still $480 and that 16 participants are expected to attend each of the two sessions, then the per participants price for each session should be $17.  $530 divided by 2 sessions = $265 per session.  $265 divided by 16 students should be rounded off and set as = $17 per participant.