Sorry I wish people stopped the whole "FreeSync ties you to AMD" thing. Many of the FreeSync monitors cost no more than their non-FreeSync equivalents with similar features. In fact one of the cheapest monitors with DP is a FreeSync monitor:
http://www.ebuyer.com/720608-aoc-g22...itor-g2260vwq6
That is under £100.
GSync comes with a massive premium,with FreeSync you rarely pay that premium.
For example,this is one of the cheapest 144HZ FreeSync monitors:
http://www.ebuyer.com/720608-aoc-g22...itor-g2260vwq6
Its £200. The cheapest 144HZ non-FreeSync monitor in the UK is £189:
http://www.ebuyer.com/670217-acer-xb...r-um-fb0ee-001
So if you are looking for a budget high refresh rate monitor you might as well get a FreeSync one even if you are using an Nvidia card.
As the cost difference is so small,or does not exist for many monitors you might as well get a FreeSync monitor if you are looking for one anyway unless you have specialist needs.
Since FreeSync is essential an AMD software interface to a VESA standard that will be introduced with more and more scalers it is no wonder the cost is probably to be not massively higher to incorporate the tech over older generation ones.