you do know we import coal too from outside, right?? :P
also, we import bucketload of copper from outside, because we have very limited copper reserves in our country, and unlike your EHV transmission lines, which are made of aluminium, the overhead wires for railways are made from an alloy of copper due to higher current they have to carry.
the savings on cost isn't as huge as you think, and unlike lines in NCR or CR this line will never see huge traffic due to its nature.
also,...
more... once you electrify, you need to setup multiple departments under electrical, which means additional cost on wage bills, plus you need to regularly cut and prune trees as these trees can get very close to 25 KV lines and can cause an LG fault if they're wet. so, we'll also end up loosing trees.