How to calculate minimum budget ?

Hello everyone,

How can we calculate minimum budget of campaign based on three keywords ?
I have no idea how to give minimum budget to the client for adwords campaign (given three keywords )
I would like to know detailed procedure how to give minimum budget to the client...This is first PPC campaign of the website.

Suggestions guidance will be helpful to me

Thanks and regards

bump
come on friends ,not even one adwords expert who can answer my question in such a large forum ?