I asked several knowledgeable folks how much it costs to build a home here in Central Florida, and the responses were consistently at $65-$70 per square foot, using VERY GOOD quality fixtures, etc, EX the land.
I ran a 2,200 sq ft home through the cost estimator, using all #3 quality materials, and it
comes up over $150 per sq foot.
I wonder what I am doing wrong?
You aren't doing anything wrong.
Using the "Cost to Build a House by State" calculator I came up with $70 per square foot for #6 Quality and, just as you did, $150 per square foot for #3 Quality,.
What one "knowledgeable" person considers "GOOD" quality my be considered very average or below average or worse to another person.
Read my pages:
New Home Construction Costs
Until you actually start getting contractor bids with explicit "Home Building Specifications", you will not be able to compare "apples to apples"