I'll drop here my 2c:
It depends (who would have thought)
This is my 5th year as a full time freelancer and I still struggle when is the time to quote a project.
What I'm doing is something like this:
First I identify how much do I need to earn monthly to live a normal life. I try to stay as low as I can and only add things I really need and not include holidays in 5 stars hotels every month and a new Ferrari every year. This is just to establish some sort of baseline and is important to be reasonable. If the average salary where you live is for example 1000$ you can't say you expect to earn 8500$. I don't say you should aim necessarily to the average salary but you shouldn't aim too far off (that's obviously just my personal opinion)
Then I decide how much I want to work. Some people think 8 hours a day, 5 days a week is a good amount, others think you should work 5 hours a day, 4 days a week. This is up to you.
With these 2 elements I can find out how much my daily rate is so if, for example, I decided that I need to earn 2000$/month I'll do 2000 x 2 / 20.
The x 2 is to include the amount of taxes I'll have to pay (and where I live is roughly 50%) in order to be left with 2k in my pockets. That will obviously depends by where you live.
/ 20 is 5 days a week, 4 weeks per month.
So with this example I'll have to earn 200$/day.
With this in mind I can price a project because with a few years of experience I know how much time a given project is gonna take me.
I like what @samnabi said about giving clients various possibilities and I also think it really depends by the type of client, if you're having fun, how much freedom you'll have working on the project, how much experience you have and so on.