Hi Gubman
You're probably looking at around €500 to build the wall 215 block on flat (labour) based on 600 blocks at 80 90 cent a block, another 250 to scud and plaster. Excavations could be done in a day depending on complexity a jcb and driver will cost you in the region of 250 for the day.Depending on the complexity of the footings if you have to step them for your slope etc ,you may need to employ a chippy to construct some shoring 250 a day. You can get rates for block costs from suppliers say around 600 for a full load of 900 blocks ,conc rates are around 70 a sq meter for 28 m I would recommend a 300 deep strip which would work out at 7 cubic metres. You would need some sheets of steel rebar cut up for the foundations ,chippy might do this for you. Difficult to know how complex the drainage may be but if its only laying some 4" drainage pipes for runoff your only talking tens of euros
excavations can be done by jcb driver when he is cutting the footings.Add 25 % if you dont want to do it yourself and want a local contractor to organise it. Again depending on what its retaining you may need an engineer to do a few calcs to see if block on flat is sufficient.