The production during December was 80 units. Demand during the first four months in the next year is 100, 120, 110, and 80. Each unit increase of production (in one month to next) costs $200, and each unit drop costs $100. If a chase strategy is followed, what is the total cost of production increases and decreases in these four months? (The first change is from December to January; the last change is from March to April)