As a contractor one of the hardest obstacles in gaining my new clients trust is help them understand the costs that go into a large remodel or flip. This might not help in your case but its a little food for thought. You can also use it as a guide to work out your questions.
Some of the things I make sure to do is:
Estimate only bid
Itemize material and show estimated cost
Estimated Labor costs
Show a low cost and a high cost (for material and labor. This way they know what they could be paying in the end)
I want my clients to know that when I give them an estimate change orders are always approved and cost is talked about before work is to be completed.
Walk them thru the entire process ( that way they understand how much work and material is really involved)
Give my client a calendar of the project
Keep the clients involved (this helps them truly understand)
One of the reasons I do all of this is when I get a new client they talk to me about there last contractor. They don't want to be hit with a large bill at the end. That is what there last contractor did to them and what they are most unhappy with...