There is a bigger issue at work here. You can pay the one professor 100K, and have a slightly more relaxed professor that is likely to be more productive, or hi

There is a bigger issue at work here. You can pay the one professor 100K, and have a slightly more relaxed professor that is likely to be more productive, or hire two at 50K that end up spending a large amount of their time looking for better opportunities, worrying about money, losing self esteem when comparing themselves to other professors that are making that 100K, etc. There is a threshold below which, you are just throwing away money.