MFT1Air to argue this from a business perspective, as you have mentioned you feel it is not sound business practice to high-ball, why do you feel it is a good business practice to low-ball yourself? When a contract gets written up, it is first negotiated. If the pilot asks for $400 per day and the owner feels it is too much he will try to negotiate a lower figure. This at least gives the pilot a higher price to start with and leaves room to shave off dollars in the process of negotiation. If you start off low then you are putting yourself at a disadvantage when it comes contract negotiation time. Why should the contractor (regardless of profession) seek to accomodate the client's interests ahead of his own? Just from a business man's standpoint it makes sense for the person offering services to come in with a high figure and for the person paying for services to come in with a low figure and best case both parties meet half way.
For the OP: sit down and run some various senarios through your head that could occur in which you would get the short end of the stick and make sure your contract stipulates some kind of protection against it. You may also want to consider being over worked. Lets say the owner needs you to fly with him for a three week trip in which you are flying everyday. Maybe there should be a clause that limits your days on without a day of rest. Just something to think about, and good luck with the offer! I'm jealous.