Check the tax records for tax rates and ratios http://tinyurl.com/njtaxrecords
Comparable property average pricing in the town is a factor as well as the tax rate and ratios being used to calculate the taxes. This is why homes selling by foreclosure or short sale for much lower prices wont generally warrant a tax reduction.
Property taxes can be appealed but only before April 1st of within 45 days of Feb 13th
The assessor is allowed a 15% +/- margin of error in their calculations.
Union County Tax Appeals page has way more details about how taxes are calculated.
Property taxes are based on various factors, such as square footage,(# bdrm's & baths), year built, and also the tax rates differ in each town. Therefore, a condo selling for around 300,000 that has 2 bdrms may have lower or higher taxes than a 3 bdrm condo selling for 300,000 in another development, depending on such factors such as the location and the year the condo was built.