The GH4 camera body(pre-order link) will be available at the beginning of May, at a retail price of 1,699 USD (there does not appear to be a version with a kit lens). The YAGH interface(pre-order link) unit for pro audio and video connections can be purchased separately for 1,999 USD, or in kit with the camera for 3,300 USD.
GH4 may be the most expensive MFT up to date but it deserves this price tag as it clearly aims at the professional videographer looking for an affordable 4K Ultra-HD video solution.
Below is the first 4K video taken by GH4 (by Bryan Harvey) that is available to public. The quality is very impressive when you choose 4K setting: