First, I suspect that you can easily get $75 per hour based on my 3rd party knowledge of the pay scales in NYC.
2nd, if this is your first time bidding this type of job (doing job estimation), I would take your estimate and double it.
So, 80 hours at $75/hour should give you $6,000.
Now it is best to never give nice round figures when you are quoting services, because people assume then that it is a negotiable number. If you have a number that goes down to the pennies, like $6,072.56, then it appears that you have put much more thought into how you arrived at your number. Be that truth or not.
I have developed formulas for calculating jobs that I do frequently, and for jobs that I do infrequently, I try to way over estimate, so that I am not stuck holding the bag. Doesn't always work, but does most of the time.
It is just hard to get started doing it, but you will be well advised to start keeping track of how long it takes to do things if you are hoping to do this in the future. Also, you need to compensate yourself for the amount of time that you spend doing things like estimating this job. As a general rule of thumb, you can only get about 6 hours of real work out of an 8 hour day. Other time is consumed communicating with the customer, answering questions, troubleshooting unexpected problems, etc.
Good luck!
pansophic