It depends on how long the Blue piece of string is.
Jokes aside it depends on how long is this project going to take 1-2 days $100 /hr a week $80/hr full time for 3 months say $50/hr = $100,000 a year maybe a bit more.
When we cost a project, civil works we would use say 3.5-5% for design on a $1 million project. How much do you value your cost savings to the client ? This may be a way of working out the rate.
Don't forget the programming time savings by spending a bit of time at start building some libraries of common functions or adding as you go, two lines of code rather than 20, also ensures that company standards are kept particuarly layers and linetypes.