I think, your proposal of running water hydrpower is generally good, but, there are certain drawbacks in the context of flat land in Bangladesh. Running water is not available all the time in Bd, and there is little water that runs in the river system during winter. A country needs power throughout the year.
Therefore, there is no alternative than to get power from Nepal, Bhutan and Burma. These countries have high mountains. Power output can be roughly estimated by multiplying Q'ty of water (m3/sec) with the Height of Waterfall (or Head in Meter). Nepal and also Bhutan both have large q'ty and high Head.
Why are you over-emphasising the expenses? Big investment will bring about output of power. This power will generate wealth in my country's factories.
I think it is a good proposal...Power generation is good investment and it will generate jobs for investor too...And apart from that India ,Nepal and BD will be befitted and interdependence will be created...