For some of my smaller spaces I want to offer design by the square metre and enable my clients to work out my fee*, which will hopefully help them to pick up the phone. The aim is to present people with a simple function so they can do it themselves, e.g. if they've got say 225 square metres what will that cost them? I'm hoping to find something people as non-numeric as myself can punch into a calculator:
area operation number operation number = $number
For the smallest area of 100m² that $2717 would work for me (17 hours @ $160 an hour) and maybe a bit less than that say as low as 14 hours], and for 300m² (the largest area) fee would be $3680 (23 hours @ $160 an hour). But those numbers are artificial (from experimenting with Excel solver to arrive at acceptable sums) and I can't get them with the same function, I don't think the answer is linear.
I do want them to be aable to enter a measure area, I'm not looking for a tiered fee structure.
*I've asked about this on ask me years ago but I now need something quite different, as my upper and lower bounds are not calculated, they are simply what I feel are acceptable charges for the work.