If you can't afford the risk then don't take the job. If it's not you area of what you do then it is better to pass.
Kinda sounds like you don't know how much time or materials it will take you. Without that your dead in the water on bidding.
Maybe it would help you more if you figured the number of days it would take x what your days labor is. Plus material, waste, warenty, MU, etc.
Don't just copy what the other guy is charging. Maybe the HO trusts your work and is willing to pay much more then $2 for your services?
