It's going to cost four figures
raccoon.onyxbits.de
raccoon.onyxbits.de
My suggestion is that you pre-authorize half-day billing in chunks as the engagement continues. Make it clear that if it is necessary to answer a single email or even think about the project, the engagement has continued and will be billed for another half of a day. Then make sure the amount you charge per half-day period is something you can live with. Before you start work on the next change, make sure they have paid for the existing bill, then get them to authorize another X half-days of engagement. Don't let them pre-authorize any more than you are willing to lose at one time, based on the amount of evidence for trust and your risk tolerance.
The initial requirements analysis and discussion session is the first deliverable which you charge for, even if it is just in a chat room.
Why do you do half-days instead of hours?
Also, it makes it less likely to get clients who are trying to milk every penny out of budgets. Which is good because that usually means the budget isn't really adequate.
Also I don't take a bunch of simple jobs. I take one or two challenging projects at a time. I don't want to encourage people to keep popping in and out of my schedule with little nagging requests.
I don't know if to people in your field it's all common practice, but I thought this was an excellent piece of writing, full of good advice. Thank you!