You will love the Charleston area, and Johns Island is a great place to live!
The homeowner's insurance will weigh into your decision on a specific home more so than the taxes.
Here's something you can do.
When you come across a property that you are interested in, go to this FEMA government site and plug the address in:
This will let you know if you are in a flood zone that will be higher insurance costs.
I recommend that you connect with an insurance agent to provide further detail and estimated homeowners/flood insurance costs, prior to making an offer.
Click this link (or paste into your browser) to view a sampling of homes on Johns Island in your price range - see something you like? Let me know when you'd like to take a look.
Feel free to search on my site: http://www.blogcharlestonsc.com
Let me know how I can be of help to you.
The Keys to Charleston LLC