Which GPU should i buy?

What should i buy to upgrade my system? i have about $450-500.

My current setup:

CPU - Intel Core i7 9700K @ 3.60GHz

RAM - 16,0GB Dual-Channel DDR4 @ 1337MHz

Motherboard - ROG STRIX Z390-F GAMING (LGA1151)

GPU - NVIDIA GeForce GTX 1080