It does not take much to get engineering to 125. Very cheap actually.

You get Draenor Engineering scroll, it is a reward from a quest or if you dont have a garrison it costs 100 gold.

Then you make the mecha-blast rocket which levels you up 3 at a time:
126 level / 3 = 42 mecha-blast rockets * 6 blackrock ore = 252 blackrock ore

Thats it, all you need. 252 Blackrock ore per toon and everyone is 126 in engineering.