I have done a few of these for myself, past clients, friends and neighbors. Working from my own personal experience, I found when determining market value for estate planning purposes one should have a thorough CMA (Comparative Market Analysis) including cost comparison be done on the property. This requires considerable time and effort from a Realtor. If you have an experienced, local Realtor you work with, you may want to ask them. If not, feel free to give me a call at 630.258.2263.