I'm time+cost estimating a semi-complex software solution, that hasn't got specific requirements in about 75% of features. I would still like to make as good estimate as possible, by getting additional data from the client. There will still be parts that may end up not being able to develop, since there's too many dependencies with other products/technologies and lack of definition. I also have a very tight schedule to produce this estimate.
There will also be other contenders on this project. Client expects a price+duration (and probably also features) and I know everyone will be off. I know that's impossible, but tell that to marketing people. Another problem is that I'm talking to middle-man and not directly to the client. I can get confidence with middle-man only, but not with the deciding client. Which is a different problem altogether.
What disclaimer/info can I put in my price plan/contract not to kill team with this project, so when project starts slipping (in terms of cost/time/features) we will be covered with some sort of payment. I would of course like to be paid by sprints or releases with relation to time, but I doubt client could be convinced in this. I'm sure we can finish this product before deadline and also create a great product, but how can I convice client to believe me?
Question
What can I do to get this project and avoid death march situation at the same time?
Any suggestion welcome!
EDIT: Outcome
In the end we (me and my co-worker) convinced the client we need at least a week to evaluate the product. So we did. We also pushed (and got) a slot for a few hours long meeting with the client to clarify any outstanding requirements' questions. So we did. Meeting was done after we made the first estimate draft, so we were sure we have all the questions to point out specifics that were either completely misunderstood or too vague to estimate. I hope we get the project, because it would mean 8 months of full time work for us, plus a reasonable pay. We'll know in about a week and a half.
Of course I also pointed out that the way we'll be delivering this product will get them exactly where they want to be with a product that will actually be what they wanted. And also that we only commit to price and time, but not functionality, because it is and will be subject to change. I think we made a good enough impression.