The most accurate way to find out the value of your lakefront home is to hire a real estate appraiser. They know the market inside and out. The appraisal will cost you between $300 - $600 depending on the difficulty of the appraiser and local rates. This can be used as a selling tool which will greatly help facilitate a sale.
Another option is to talk to a qualified, licensed and experienced Realtor. They can prepare a Broker's Price Opinion (BPO). It is less accurate of a report but it will give you a good ballpark to work from. Generally this report is free or nearly so.... more