Your best bet would be to have a local Realtor view the property and provide you with a current Comparative Market Analysis (CMA). This would take into account the fact that it is a seasonal property, the location, properties that are on the market (your competition) and ones that have sold.
Your Realtor should be able to assist you with finding out from the city if the home is allowed to be converted to year-round as well as assisting you in contacting a reputable contractor to give you a estimate on converting the home for year round use. This would be great to have on hand for potential buyers to review, as most will want to convert to year round use in our area on the shoreline.
I would try to get it on the market as soon as possible to try to take advantage of the remainder of this summer season when buyers can see the benefits of living at the beach. It will likely spend more time on the market if you list it during the fall or winter. Spring to Summer is the best time to sell beach properties here.
If you would like preliminary information on what is currently on the market in Branford I would be happy to email you the list so you could get a rough idea of what properties are going for. Feel free to contact me by email or phone. Kimberly Bailey Madelung