I can't tell you precisely, but I'd imagine it's not worth it.
The ABS system seems to have a lot of extra/different parts. There are wires, pipes and sensors all over the place, the disks I think are different too, they have the slots for the sensors to read. You'd also have to check the loom is the same, mine has an ABS warning light so if the wiring for that is not already in the loom you're looking at a major overhaul.
If adding ABS was a plug-and-play operation, Yamaha probably would have opted that as an accessory. Instead they chose to make a different version out of the bike (MT-07 vs MT-07A). I suspect the whole wiring loom is model specific, as are all the brackets etc (not to mention the ABS-stickers on the fenders).
