As has been mentioned, by Russell and others, there are two ways to approach it – with the stacked walls (keystone type) and with engineered walls.
We have a lot that slopes down from our house – and built a companion unit and a switchbacked handicap ramp down to it. We have both engineered walls and fill, as well as the stacked walls (on the ramps.
The cost of bringing in fill, or removing fill can vary widely… But it can get expensive depending on how many yards. There is an entire sub-industry of moving dirt in San Diego county.
