Summary: Cost depends on how deep the line is at 100' away from the house. and if the plumbing contractor digs the hole or if you dig it. $2,000 is a reasonable price.
Cost depends on how deep the line is burried at the point they want to fit a new access point...
If the line is 2 feet deep at your home, and slopes 1/4" per foot, then in 100 feet it is 5 feet deep where they will have to cut the line and fit a wye...for the clean out.... that is a fair size hole about 6 feet deep and 5 feet wide, they will have to bring equipment in to dig it.... its a two man job for one day...cost of labor with insurance, social security tax, bonds and over head etc is in the $60 to $80 an hour range... so you are looking at maybe $1,500 for labor expenses, plus equipment rentals, overhead and profit.
If you dig the hole yourself you can save at least $1,000 of that... you can hire that done by casual labor for $300 or $400 by hiring men that work out of the Home Depot parking lot.. there are more than a few risks in hiring unlicenced casual labor however. You could also rent a back hoe (small tractor with a big digging bucket on it) and dig the hole yourself, half day rental would run a few hundred dollars. The risk is that you could hit a buried electrical, gas or water line.... you would have to check with the local utilities on the location of their underground pipes.
The clean out wye installation can be done by one man in 2 hours or so and with about $120 in fittings, that will save you a lot of money.
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