How to write an estimate for the development of a site without a clear understanding of its concept?

Question

Preparation of terms of reference

The situation is as follows: there is a good opportunity to fit into the development of a very large project, but before the final signing of the contract, the beginning of the preparation of technical specifications, etc., the customer requires an estimate. To be honest, I have never had to work according to such a scheme before, but dictating your terms to a serious customer is fraught with his refusal, which I would not like very much. So the question is, how to make an estimate and not be fooled, if there is no complete understanding of what and how? I understand that the situation is a bit idiotic, but it happens ...
Thanks in advance for the tips!

Answer 1

well, standardly overprice to fit in exactly
and you will have an estimate,
and when they ask why ask for it

Answer 2

Correctly. Take money for the preparation of technical specifications. Then draw up an estimate and take the same money for it. And there you will see what and how much.