I could see at least three levels of service:
- Buyer does all diligence just want a second set of eyes. Could be by hour or flat rate for up to so many hours of offsite review. $500 to $3000
- Third party would oversee all diligence for water and sewer and put together global report but would not due onsite work. $4000 to $7000
- Third party would due everything in level 2 and probably have 1 to 3 days of onsite diligence as well. $8000 to $15000. Buyer would cover travel expenses and per diem of $1200 for onsite and $500 for travel days. I think the $15k would cover everything except travel expenses on a three day onsite deal including per diem.
Buyer would still be responsible to pay for third party inspectors such as video, sewer tank pumpers, plumbers, well or pump guys... you get the idea.
I think the above prices are in the right neighborhood.
These sorts of things tend to be huge time blackholes so a cost not to exceed would be the way to go for the buyer but not so good for guy doing it
To do a system with a lagoon the lagoon should really be cored to see depth of biosolids (tons to dispose of) and collect bulk samples to test for heavy metals. If your over the limit you have no way to dispose of the biosolids. Think supper fund site. This would eat a whole day.
Just thinking out loud here.