(x-post /r/personalfinance) Soon to be homeowner, how can I tell how much dwelling coverage I need?

My fiance and I are in the process of purchasing our own house and one thing I'm trying to figure out is home insurance, specifically reconstruction cost and why there are so many different numbers. For instance:

• American Family - reconstruction cost $172,000

• Nationwide - reconstruction cost $235,000

• Liberty Mutual - reconstruction cost $140,000

• Farmers - reconstruction cost $206,000

• Actual purchase price $117,000 and appraisal is $140,000.

I just really don't understand how they, with the same information, can come to a drastic range of numbers as to what they think I should have for coverage. Is there a way to tell what I actually need?