"To do this locally, we could probably get away with paying at most £70,000 for the disks, enclosures, servers and the associated electricity costs over three years"
Someone hasn't got a clue. You would expect to pay ~£15K+ a year just for a rack + power in a decent datacentre.
Then the hardware costs are usually only 20% or so of the lifetime TCO....the 200TB of storage alone will likely set you back circa £70K.