If we're gonna make this work, you gonna need to understand few simple rules.
First of all - i might adjust your idea (obviously talking to you) if i don't see enough creative input from your side or directions given are too vague.
Second - once art piece is done and we strike a deal, you pay for the work and receive art piece - that's it. If you need further support of the art asset - we can arrange additional deal.
Third - I do make a discount if work is considered non-exclusive (I.e. you get royalty free copy but i keep ownership with possible re-selling rights to myself).