The G-Sync cost is due to a few reasons.
- It's a proprietary product.
- It requires a physical chip on the monitor end to talk with the video card. (That may have changed, but it did when it first came out. It's been awhile since I've looked up how it works now.)
- r&d for the thing... since it's still "relatively" new.
AMD's Freesync is more consumer friendly in the sense that it doesn't require additional hardware outside of the video card to make it work. So it's a lot cheaper to implement. But the actual tech itself I would say after witnessing both G-Sync and FreeSync in action, the G-Sync is a more mature product? But I think that's just due to the limitations on the Freesync end. It's cool to have either FreeSync or G Sync, but it's not the end of the world if you don't use it.