just to be sure, is it added network fee in their calculator(fixedfloat.com)?
It's a business mate, do you want them to cover even your transaction fees?
How sustainable would that business model be, even after giving very competitive exchange rates?
is it possible that they can provide btc network fee less than dollar?
Yep, if the mempool size is so low like it is usually in most weekends.
if not, how can i figure out how much it will be
Use mempool.space to know the optimal fees and current state of the Bitcoin network