Originally Posted by clementine

I'm just a builder but same applies:

As Eric said,

Estimate how many hours to do the job x your hourly rate + extra labour.
Add removal of waste.
Add overheads like fuel, insurances, office, gear and equipment.
Add a bit for profit.

If you don't get the job go a bit lower next time. If you do get it and loose money, go a bit higher next time.
If all goes well you are in the ballpark.