The thing about 1440p from 1080p is that the bigger monitor screen you get the bigger you're going to want your resolution. Monitor sizes of 27" or more you will need 1440p if you don't want the screen to possibly look a little blocky/blurry, as some people report, since the resolution will be too low for the density of pixels.
Anything under 27" you can get by with a 1080p no problem. I went from a 1080p 21" to a 1440p 32" and the quality does not look any different because the screen is big enough to accommodate the pixel density and resolution.
Anywho, you're gonna have difficulty finding a decent 1440p gaming monitor with g sync since g sync is a preimum cost. You can simply get freesync and it'll basically do the same thing even if you have a nvidia card. In fact some monitors are approved by nvidia to be gsync compatible even if it's a freesync based monitor.
https://www.microcenter.com/product/609322/CQ27G1_27"_QHD_144Hz_HDMI_DP_FreeSync_Curved_LED_Gaming_Monitor?storeID=115&gclid=Cj0KCQiAnL7yBRD3ARIsAJp_oLYNlXSfH-U7VJDfsjwsCs8MQQqlIROmPa0EjFh-lI0HGJsU4ZKDpw4aAou8EALw_wcB
Here's one monitor that's within your price range. Though if you don't care about color quality, then you should also look for monitors that are TN panel based.
There are 3 types of panels to look at while you're getting a monitor:
IPS (Best color quality but the most expensive and harder to get high refresh rates)
VA (middle ground between IPS and TN, not as good as IPS in color and view angles but is able to achieve higher refresh rates and has a deeper contrast for blacks.)
TN (Has the worst color quality and viewing angles but is able to achieve the fastest refresh rates. Is also the cheapest panel types.)