The best budget graphics cards come from a range of GPU manufacturing generations. You can use one of them. Hope its gonna work for you.
The first recommended Graphics Card for playing Fortnite is EVGA GeForce GTX 1060 6GB SSC GAMING ACX. 2. EVGA GEFORCE GTX 1070 FTW2 GAMING, BEST AFFORDABLE GRAPHICS CARD FOR FORTNITE
GeForce GTX 1070 comes with 9 additional sensors embedded on the PCB monitor memory and VRM and has a RAM of 8GB.
XFX Radeon RX 580 is a pocket-friendly Graphics card and has a RAM of 8 GB.
Chosen by over 20 million gamers, MSI GeForce GTX 1080 was nominated and voted the best graphics card of 2016.5. GIGABYTE GEFORCE GTX 1050TI G1GAMING 4GB
RTX 1050Ti has a RAM of 4GB and integrated with GDDR5 128 bit memory.
ASUS ROG Strix GeForce RTX 2080Ti is quite expensive but I assure you, it’s worth every dollar.
EVGA GEFORCE GTX 1080TI can handle Fortnite on ultra settings.