check this link
http://www.microsoft.com/sql/prodinfo/features/compare-features.mspx
as for cost, who do you normally purchase licences from ?
Give them a call and get a quote would be best?
Basically Ent allows online indexing , max CPU and Memomry support, as well as other business intelligence options,etc
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"Ya can't make an omelette without breaking just a few eggs" 😉