The Madness Engine by Slightly Mad Studios already supports the XB1/PS4 platform.

Is your question about what it had cost them to become XB1/PS4 ready? You'll have to email them to find out.

If this is for yourself, then you'll have to "shop" around for (small) studios that may be interested in porting your game to get estimates.

Do you hold the license for the game you intend to port?