That looks really nice. The foundations need to be very deep and wide because of the short terrace between combined with the steepness. Sorry, don’t
know how much it would cost. The only engineered retaining wall I ever had my hands on was approved by the time I got involved and I only did the foundation. The owner then hired a mason and his helper for $5OO a day(probably $400 now) and did the water proofing drainage and backfill himself with the help of a bobcat opperator who he paid by the hour. He saved a ton of money vs hiring a top notch hardscape guy and got great results.