$125-$150 per hour for C++ developer?!?! seriously?!
An average wage is $42/hour. The highest is $96/hour.

see https://www.payscale.com/research/US/Job=C%2B%2B_Software_Engineer/Salary

TOTAL CONFERENCE BUDGET (ONE-TIME) $74,320

WTF?! This is absolutely NOT necessary for development. It should be a separate proposal or a personal decision of the developers, if they want to spend their OWN money from the salary.

Your proposal is very inadequate. It needs to be revised.