I install 1000's of feet of gas line a year.Use 1 1/2 PE[yellow poly] and dig the trench.I dig in rock conditions often.It is hard work but with a good trencher with at least 16hp you should be able to get it dug.Dig at 20" min.Check with a rental yard and see if they have a ditch witch rt16 or rt20 for rent...it will dig it..your local wholesale plumbing house should have the PE and the meter risers and your all set..cost should be under 500 total