Retaining Wall, Cultec Plastic Chambers, Leveling... Cost?

The lower level of my tiered backyard is approximately 40x15. We are having someone build a 5 foot retaining wall along the 40 foot side and then the landscapers want to use 2 Cultec Plastic Chambers for drainage. They will filling to level our back yard and then by planting 8 foot Arbovitae along the 40 foot side. How much should I expect for this job to run me? I live in Westchester, County, NY, where things tend to run fairly expensive...