It was my curiosity to know who pays the money for hosting a presidential debate and how much it costs. CBS news article gave answers. Universities ( this year they are: University of Mississippi for the first presidential debate, Washington University in St. Louis for the VP debate, Belmont university for the second presidential debate and Hofstra University in Hempstead, N.Y for the third one) that wanted to host a presidential debate had to be willing g to pay $1.35 million to cover production expenses and millions more for facilities and other associated costs. Did it worth the money? Schools say yes.
If you are interested in the site application process, read Commission on Presidential Debates (CPD) site selection guidelines.