I am in the landscaping industry and have a long, complicated spreadsheet for calculating estimates and was hoping to find an answer for a formula to calculate escalating costs, for example (numbers are not actual):

for a lawn fertilization it is $50 for a 4,000 sq ft lawn, $53 for a 5,000 sq ft, $55 for 6,000, $58 for 7,000, etc. etc. etc.

I used to use a flat rate cost per 1,000 sq ft but when you get to large properties the cost is so high and unwarranted given the efficiency factor i.e. cost per 1,000 sq ft should be lower for large properties to make it fair and competitive.

Any recommendations???