It would depend on how far committed you are to the property so far.
I would talk with the sellers to find out to what extent they would be willing to let you have the lot tested prior to purchase.
I’m currently in a similar situation in west Knoxville. I’m purchasing a lot in the Deane Hill neighborhood and discussed with the sellers that I was willing to 50/50 for a land survey and soil survey. Knowing the area, the demand in the area, and the neighborhood comps I know that any thing short of a potential sink hole issue, and the lot was a no brainer. All of these terms were contingent on my 50/50 portion being converted to earnest money in the event that they were to accept an offer from me.
I would recommend that you push for the appropriate soil surveys (also land survey) to make sure that the rock you’re dealing with would me minimal in the desired build locations.
Otherwise I would be extremely careful when dealing with rock. The septic systems are fairly straight forward and can range between 4500-6000 dollars per unit supplied and installed. The well system is another matter entirely. I’ve estimated them before where they can exceed $10,000. It all depends on depth, undulation, and footage to run said water.
If they agree to the surveying and testing it would be worth the 400-500 dollars to find out if you are about to lose your butt, or if it’s a good deal.
Just as a point of reference to my experience. I’m part owner in a residential construction company that has been active for 10+ years, and I’m also an estimator for a national log home building company located out of East TN/Knox, so I’m fairly experienced in the cost of build area. I’m also a soft wood lumber salesman for the east TN region supplying 2 x materials and other boards from the southeast.
