In New Jersey it is not mandated that square footage be posted on MLS or any listing information. Therefore, the sq foot is often omitted or it is inflated to make house appear larger. There is no real way to get an accurate or even close estimate of sq ft in NJ to use as an accurate measurement.
That being said, I disregard all averages that include sq footage unless you know for certain it is accurate.
I am also not sure what you mean by the same as sale price. If you are assuming a 3000 sq foot home multiplied by $193 should sell for $579,000 then the logic is seriously flawed. There are a lot of factors that are taken into consideration when pricing a home. Some are bedrooms, bathrooms, finished basement, flow of house, condition of house, upgrades, pool, landscaping, lighting, location of home, and more. There is also a consideration about what is next door, is the street a busy street, is commercial zoning nearby and on and on. All that factor into price of home.
You really need to visit the property, interpret the home and location, condition of home and all those other contributing factors then do your research on comparable sales to calculate an estimate. This is sometimes more of an art than a science.
Hope that helps