US planes are expensive. But, at $35million a piece 48 units of F-18 Hornets will cost around $1.7 billion, and not $4billion. Yet, it is a big sum of money, but today's Bangladesh can certainly afford these. Payment will not be made in one single year, I believe.
Do not also get misled by our defence budget of about $1.6 billion. This is for salaries and maintenance. Weapons are purchased according to our need and availability of foreign currency. It is unrelated to the defence budget which is spent in local currency. Weapons is something like purchasing rice from abroad. Rice purchasing is not covered in the budget. We pay in dollars and rice comes in. It is same with weapons.
BAF has not yet decided which planes it will induct. I have heard that it is also considering SU-30 or something better. Note that the present govt has better relations with Russia than it has with USA. As it was before, this time also USA may refuse to sell citing a case of poor BD.