I second that, since you don't know what you're getting into. The people who
charge a fixed fee have to know what they are getting into. If you don't,
you have to use a different approach.
If you have to give a fixed price you need to:
estimate how much time it will take
have a $/hr number in mind for your time
factor in your overhead in $/hr
have a contingency built-in
factor in some profit for your business
Also draft an agreement that limits the scope of your work, and protects you
from scope-creep and makes the client pay for alternates, changes of mind,
unknown approvals processes, etc. and get them to sign it. I recommend
including a schedule of payments linked to demonstratable benchmarks, and
stay one payment in advance in case the clients drop dead, change their
minds, or try to stiff you. Specify an hourly rate to apply to work done
since the last payment in the event of termination of project cancellation.
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