This is the problem I have at the moment as well:

Company Leadership asks for estimate with barely any information, I will then say that I need to learn more about the project and look into the codebase, leadership then says that they "just" need to have an estimate to approve this work and if they want to do this project at all. Around and around it goes until I give them a large estimate (which is large because of all the unknowns including the unknown scope) which is then too much and too expensive for leadership.