Only advice I can give is to bid the job like you have tons of work and you are following standard procedure.
In my first year of business I can look back at the invoices in relation of time where I was struggling to make ends meet and stop the borrowing....and every job I took out of desperation, I lost my ass completely and to this day I don't do work for the clients I got the bums rap on.
It was tough no doubt and hope I never end back up in that situation again.
What I'm getting at is if you low-ball that bid, you'll spend a good deal of your time exchanging money in your accounts with no real profit to speak of. Everyone needs to make profit and small margins drive you out of the biz.