“Your major” exists at virtually every university in the country. You may need to do an independent study senior year, you may need to craft an interdisciplinary program out of three different departments and find a faculty member to sponsor you, but there is nothing exotic about what you want to do.
Don’t get sucked in to the nomenclature and marketing, especially if you have financial constraints. Look at any university with a strong political science, foreign affairs, regional studies (depending on the part of the world you are interested in) and take a look at the course catalogs to explore the crossover with econ, history, and the other disciplines that are relevant to what you want to do. Agronomy is particularly helpful for the Peace Corps but that’s usually a strong department at big flagship state U’s. But a strong geology, earth sciences, public health, bio, chem, can give you what you need.
Which of these U’s are affordable with just need based aid if the substantial merit awards don’t come through?