All prices are local. See what similar cars are selling for in your area.
KBB private party sale value where I live in the Midwest for a 2001 LS UL in that color with that mileage in Good condition is between $4,916 and $7,245 which I think is unrealistically high.
A 2006 LS UL with similar miles in a more desirable color with the optional PCS/DRCC package could bring $10K to $13K here if it is in KBB Good condition.
It's a shame these cars aren't worth more but there isn't much demand for old Lexus sedans - even originally expensive ones.