Here is the government report on Large Power Transformers (LPT). It gives the cost which will astound you, plus tell how long it takes to get one and tell you we are trying to start making them ourselves. Read page 6 and 7 for sure.
http://energy.gov/sites/prod/files/Large%20Power%20Transformer%20Study%20-%20June%202012_0.pdf
Thanks. That was a rather sobering read! Makes eighteen months sound like the extreme low end for re-up time.