+1 for go to a ground works contractor.
Wouldn’t have thought that many would have ready access to an excavator with a reach like that in the picture above. Most should get 14m infront reach and maybe 9m down but you obviously have a big bit in the middle out of reach.
I’d think your bet bet would be to dig down through the cliff with the excavator working in the trench made, obviously with proper temporary works in place (properly designed) then as you tech down to the beach side dig that with an excavator in top. Once again temp works is key due to the probable nature of the ground.
As mentioned that’s a lot of earth to shift. A rough guess would say 7500 cube meters, if you cannot leave that on site then that’s 800 odd wagon loads!