Why? Just stating the facts. Are you considering 2 Ohio class submarines for a budget of $100 million USD? Neither will Chinese sell their Song class SSKs to Bangladesh.
The GoB has not yet declared the type of submarines and their source, although all of us assume it is from China. BN has just started to plan a submarine base probably in Mognama near Cox's Bazaar and Sonadia. It will take at least three years to acquire land, do survey, do design works with the technical help from selling country's navy, and build and operate the base. Many things will change and a rising BD economy can then afford a submarine better than even Song class. So, wait for a few years only.