well thew s5 cost 300 now or 350, i doubt it was the case an the beginning, so yes it can be depreciated quite a bit
S5 is now a generation old, majorly less efficient than either of the new miners commonly available - and I've not see it at $350 since the BTCC-inspired Bitcoin price spike. I've been giving serious consideration to selling mine off NOW when I can do so at a profit - not even factoring in the amount I've managed to mine with them - and putting the resulting coin into another investment I'm working with right now.