It used to be that engineers cost more as Mk. lvl went up, including energy costs, which engineers used to have. Because of this, people saw little reason to get them, as 2 Mk. I engineers can do more than 1 Mk. II engineer for the same cost. So, they made the costs of engineers inversely-proportional to Mk. lvl to encourage their use. Then, later, they removed energy costs, and as noted, all engineers lost their teleportation. People wined, so they gave Mk. III and Mk. V engineers their teleportation back, but increasing their costs to offset it.
Now that the energy costs are gone and repair and construction rates can now be tweaked separately, maybe its time to make costs of engineers scale linearly again. (And now you know more about the history of engineers than you ever wanted to know.
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Edit: Note, linearly does not necessarily mean Mk. II costs twice as much as Mk. I. For a linear relation between x and y to hold, there must be an a and b such that y = ax + b holds. If y is cost, x is mark level, a < 1, and some some suitable choice of b, then there can still be a linear relation but cost(Mk. II) < 2 * cost(Mk. I)
