Compute Module 3 shares the same basic specs as the RPi 3, which is to say it includes a Broadcom BCM2835 SoC clocked at 1.2GHz, 1GB of memory, and 4GB of on-module eMMC flash. The company is also releasing a "Lite" version (CM3L) that moves the SD card interface to the module's pins so a user / company can wire it directly to an eMMC or SD card.
In addition to the CM3 and CM3L, Raspberry Pi is also releasing an updated Compute Module IO board, named, you guessed it, CMIO3. This board gives you the platform for which to use your CM3 or CM3L, and also provides the ability to rewrite CM3's flash memory. Further, it includes HDMI and USB connectors, and even supports the original Compute Module, if you happen to have one kicking around.
At the moment, pricing for the CM3 is ~$32.50 USD, ~$26.50 USD for the CM3L, and ~$115 for the CMIO3, based on pricing at the UK website RS.