I recently found this AWESOME site a few days ago. My formula for a rough bidding price is the total square foot of the property x 2 then divide that number by 1000. Example a 120x70 lot is 8400 sq feet x 2=16800. 16800/2=$16.80 Let's just say $17.00. Add a 15% mark up and you get $20. Depending on the number of trees to work around, amount of trimming etc., I adjust accordingly. I only do residential property now so I don't know if it would apply to a commercial size property. Do you guys recommend a flat rate ie. up to 9000 sq ft. $25, 9001-12000 sq ft. $30.