My daughter told me a relevant joke: A university's Dean of Research became frustrated during budget negotiations with the science faculty. "Why do you physicists always need such expensive labs? Why can't you be more like the mathematicians? All they need is paper and a waste basket."
After a moment he added: "Or like the philosophers? All they need is the paper."
Yes, philosophy is cheap in terms of material resources. It is worth adding that the journals and books tend to be cheaper also, compared to other subjects.
However, teaching philosophy is often an intensive, small-group experience -- so that costs. More importantly, like any other subject, the researching philosopher needs TIME. And time is comparatively expensive, with respect to material resources.