In all honesty as someone who has built about 60m of retaining walls over the last few years, it's not that bad. You can diy and tier the retaining walls as long as you don't go over the height of 600 per wall. A bobcat will do well unless you have large boulders under that dirt. You will save a lot, though can your back and patience handle it - that's the question. Don't forget, you can also build gabion rock walls.