Burying 8 inch Pipe With a Cat 215

I am trying to come up with a rough estimate on a per mile basis. The job would entail digging down 4 feet and burying 8 inch water pipe and covering it. The dirt is very sandy, loose material. Easy digging, but sand falling in would be an issue. We have an EX400 on location, but it's too big and we would have to buy a smaller machine. A Cat 215 is what we had in mind. I'm not familiar with trencher machine capabilities, but that could be an option as well. I know that these estimations are extremely difficult, but what I am mainly asking for advice on is:

~Running Costs on 215 Sized Excavator
~The running time it takes to dig in 4 feet and cover over in loose sand (not including pipelaying time)

Other useful info would be:

~Cost of 8 inch plastic potable water pipe
~Trenching machine or other excavator options

Thanks!

Burying 8 inch Pipe With a Cat 215