Hi
So for your first question that which card performs same as GTX 770 but it must be a new one. It's the GTX 1050 Ti, new architecture and less power consumption too. And a bang for your buck card. It's prices have raised however and not good to buy it new right now but buying it used can be a good decision as people are selling it for around 150$ used. It is just a slight better then the 770, else they perform very same.
But, if you are looking for upgrading. Get the GTX 1060 3GB. Its 70 percent faster the GTX 1050 Ti and GTX 770. But buying it new will be non sense due to its very high asking price. Look for used ones which have warranty but go for cheap or price you want them to be.
I hope I have given satisfactory answers to your...