Fixed price contract = the bane of many. To accept a fixed price contract you have to
1) spell out in agonizing detail what the contract covers. "Updating system X with function Y" will invariably cost you unpaid hours. I need be "providing system x with (50 lines min description)"
2) specify that any request/requirement/change will be billed at $xx per hour.

In my beginning days, I goofed on the above and managed to make $0.83 per hour on a large project.

Erik