Wendy, that difference would seem about right to me.
Best thing to look at is what comparable CYVs have actually
sold for recently, say in maybe the last year or so. As long as you're comparing apples-to-apples as closely as you can, that would give you a fair take on what current market value would be - give or take based on lot premiums, upgrades that add value, and so on. Compare the one you're considering to others in the same villa group (or others close by) that are of the same or similar floorplan that would be comparable - there are lots of variations in CYV floor plans/square footage that impact pricing.
Actually, it's kinda a good thing that the county comes up with assessed values that are lower than the going sales rate - helps you on your property taxes!
Hope that helps -
Bill