As of today, the Oracle Database 12.1.0.2 with InMemory Columnar Store is available at https://edelivery.oracle.com.
According to the price list of July 10th, it will be sold as an option for Enterprise Edition (Exadata NOT mandatory), for US$ 23,000 per CPU (calculation like EE).
Hope it will do well, beta demos were extremely impressive.
Yours
Martin