iPad 3 will be launching in US, Canada, UK, France, Germany, Switzerland, Japan, Honk Kong, Singapore and Australia on March 16th 2012. The prices for the WiFi/4G version of the device is similar to the iPad 2.
Apple will begin shipping the iPad 3/iPad HD device on March 16th. However, as a user you can start pre-ordering the iPad 3 right now. To pre-order the iPad 3 you can visit the the Apple Store at http://store.apple.com/us/browse/home/shop_ipad/family/ipad.