Since you have never lived in this beach house, it would not qualify as your permanent residence under the definition of the IRS. Therefore there would be no exemptions allowed on any capital gains that you recognize as a result of the sale. Whatever your net gain is on the sale of the home is what you will be liable for on the calculation of long term capital gains tax which is currently capped at 15%.
As far as determining what the property value was in 2003 when you inherited this home, there could be a couple of things you could try. First, if an estate tax return was filed for your father, the value of the home should have been included on the estate return. The second thing you might try is contacting the county assessor's office where the home is located to see if they can tell you what the property valuation was back in 2003. You might also try contacting the insurance agent that carries the property insurance on that home to see if they have records of what the home was insured for back in 2003. If none of those sources are able to help you, then you might try contacting a local real estate agent in that area for assistance. Basically what you need to do to determine the fair market value is to come up with a price that the home could have reasonably been sold for back in 2003, and a real estate agent would probably be able to help you with this if the other records I mentioned are not available.
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Thanks again, and let me know if you have additional questions.