On one level, this really isn't that outrageous. The plans also include a big natatorium that will serve a couple of districts. Also, when you build a stadium that seats 12,000 (and they do need that capacity), you get a big difference in lifespan depending on the engineering. You could save money by building a pretty bare bones structure, but it would not last nearly as long. Prosper ISD is in a very fast growing suburb of Dallas. They are planning on adding a high school in 2020. So, this will serve two football teams and probably be available for games for a couple other districts that do not have good stadiums. Plus, it is paid for with bond money that voters approved, not by taking funds out of the school's budget. $48 mil is a lot of money, but the annual budget for Dallas ISD is about $1.5 billion. I am sure they could do a lot with $48 million, but that amount of money would not end the big differences in quality between inner city schools and schools in the burbs in Dallas.
But if you took $48 mil and all the other money spent on HS football and used it for other programs and services at Prosper ISD, you could make a huge difference in the outcomes for many students. Even at wealthy suburban districts like Prosper, funds for counseling, special education and other social services are very limited. There are lots of AP classes and opportunities for high achievers, but the resources dedicated to kids who are struggling academically are minimal, especially in comparison to what is spent on football. So, yeah. I a globally competitive world where entry level jobs for high school graduates (outside of the very unreliable oil patch) do not pay a living wage, there is definitely a case to be made that spending priorities on a $48 mil stadium are out of whack.