Products evaluated
ATG -> Java
DemandWare
IBM Commerce - Java
Magento - PHP
Demandware operates on a percentage of total revenue, usually around 2%. ATG, Hybris, and Intershop all vary from $60K - $250K, plus development costs.
My personal opinion: the large proprietary packages aren't offering much more than you get from open source such as Rails Spree or Piggybak, or other 'no-licence-costs' platforms.