Need to dig and install drainage lines

Los Angeles CA

Description

I need to install two new drains in my rear parking lot. For each of these two drains, we need to run 4" lines (each about 40 feet) across the parking lot, merging into a 4" line that you would install down the driveway (about 100 feet) to the street. We already have an existing line that goes under the sidewalk to the street, so we will connect to that. The parking lot is asphalt, so that's 2 drains and a total of about 80 feet of 4" line under that. The driveway is dirt, although very rocky. There is a total of 100 feet of new line we need there. So the grand total of new pipe is 180 feet. I have attached a drawing to show the layout. Ideally, you have some experience with this and can do the job fairly quickly, since we will be repaving the entire parking lot and driveway soon. This is not a huge job, so it's probably not worth coming here for bids. So instead, give me an estimate based on my description of what you think it would cost. Then I'll hire based on that, with the agreement that if there are unexpected elements when you actually get here, then I'll pay whatever good faith additional amount that would be.