There are a lot of options there, but the word budget doesn't come to mind. There are some reasonably priced ones... in the $200 range even, but when most people think of budget monitors they think of $100 monitors.
Now if you've got an AMD video card, pick one out with FreeSync. If you have an NVidia video card you should consult NVidia's website and find out if there are any monitors in this price range that are FreeSync but certified for GSync. If you have to go with a native GSync monitor... well, lets just say that we will be moving further from the word "budget" in that case.