Coles Washington DC trip for school

My 15 yr old has an opportunity to represent his high school at the National Student Leadership Conference. He wants to attend the conference for Aerospace which is in Washington DC.  Its an 18 day program. He will stay in a college dorm and get the full experience of a college student as a freshman in high school this is an amazing opportunity for him. It will cost several thousands of dollars to attend. To attend this 18 day conference it will cost $3,500,  plus must pay for his own airfare round trip,, plus a commuter expense of $850. Plus eating expense, spending money and he will need new clothes, and other essentials to make this a successful trip. We are beyond proud of him.   Spots are filling up fast and he must have deposit of $350 in as soon as possible. I can't determine the cost of airfare as prices change constantly.