It is the word reasonable that is a value judgment. We have members here that due to their location have restrictions on what they can buy and at what price. So to them buying a Arduino Micro would be unreasonable.
As you will probably want to use one sensor per block, and not want a wire to each block then you would be looking for a proper capacitive sensor (not the Arduino library one) and some sort of radio connection, like a BlueTooth module.