Mark is spot on - basing your value on any formula pertaining to assessed values is a dangerous game. Initial asking price isn't much better, either. Value is determined by what somebody is willing to pay for it, and looking at recent sales in the area gives us a good gauge for what might be expected.
We offer a free service to get a bird's eye view of real estate activity in a given neighborhood - what is for sale and has recently sold, as well as how long it took to sell, how close to asking price, etc. Go to http://www.CapeCodHomeValues.info to plug in the area you're looking for. It will send you a free report right to your email. Our clients love it.
Buyer's dictate markets which means you should offer what you are willing to pay for the home and the value range is a way to manage expectations.
Try not to focus on the assessed values as they are not even close to being a strong indicator of market pricing. Give me the basics of your search (eg. cape/ranch # bedrooms, condition, town etc.) and I will give you some ballpark ideas as to what those properties are selling for. As neighborhoods can vary from block to block, it is a very dangerous way to determine value. Are you interested as a primary, or second home?