Producing quality extra virgin olive oil is a labor-intensive process. Making one liter of oil requires 5-8 kg of olives, which often must be hand-picked.
Small Italian producers often do all the work — from growing to pressing — by hand. Mountainous terrain with olive groves doesn't allow machine harvesting.
Cheap olive oil (under €5/l) is almost certainly an industrial blend, often of questionable origin. Investing in quality olive oil is an investment in health and flavor experience.