Ok, I know that as a pump n dump system where you're not returning any water back to the source.
FWIW the return wells always seem prone to plugging. The hardness in the water will drop out in low pressure situations (like after a CSV), eventually causing the return well to lose acceptance rates and generally making a mess in the yard.
That was why I asked about water quality.
Cost for a return well....I'd be about $6000-6500 for a 370' well, fully cased and screened, gravel packed, grouted and developed.
$6000-$6500 sounds more than fair to me, but I know the mentality of most homeowners. If they can't see it and show it off, they probably won't spend the money to have the job done right.
LL is right about clay being a poor conductor of heat, that's why they have to put so much sand in the grout when grouting in the loops.