This whole question may puzzle the volunteer who knows that the equivalent time donated in an affluent country may be worth many fold the expenses under consideration. However, most relief operations have very limited budgets, and they simply can not afford to pay these expenses. If they had more money, they could probably hire some additional local help instead. In reality most short-term volunteers give more than just their time. They often pay their own travel expenses.
Many volunteers find sponsors to defray expenses of volunteering.
Colleagues at work, religious groups and families are frequent donators. Usually the cost of travel while performing volunteer duties for a tax-exempt organization is deductible. The value of the voluntary service itself is usually not. Obviously, the answer to this depends on individual circumstances and time constraints. For many people short-term volunteering is best to begin with because they will have a chance to see if they are suited for this work or whether a particular assignment is a compatible one.