The prices of video cards are at an all time high atm due to the extreme shortage (COVID + mining craze) but you can use your current gpu for now and add a new (modern) one to this build later on once prices get back to normal. Easy as pie to build this yourself thanks to youtube or have a local PC shop put it together once all the parts arrive. Match these parts on Amazon for the free shipping.
This gives you an idea of what your looking at price wise for a modern gaming PC minus a new video card.
https://www.newegg.com/black-fractal-design-focus-g-atx-mid-tower/p/N82E16811352069
Fractal Design Focus G Black ATX Mid Tower Computer Case $55.99
Exhaust fan for that case.
Buy ARCTIC F12 - 120 mm Standard Case Fan, very quite motor, Computer, Push- or Pull Configuration, Fan Speed: 1350 RPM - Black/White: Case Fans - Amazon.com ✓ FREE DELIVERY possible on eligible purchases
www.amazon.com
ARCTIC F12 - 120mm Case Fan $5.99
https://www.newegg.com/super-flower-leadex-iii-bronze-sf-550r14he-550w/p/1HU-024C-00016
Super Flower Leadex III Bronze PRO 550W 80+ Bronze Modular Power Supply $64.99
https://www.newegg.com/p/N82E16813119385
ASUS PRIME B560M-A $110.99
https://www.aaawave.com/intel-bx8070110400f-core-i5-10400f-6-cores-up-to-4-3-ghz-desktop-processor/
Intel Core i5-10400F $156.99
https://www.amazon.com/DEEPCOOL-GAMMAXX-Heatpipes-Motherboard-Control/dp/B08C231WQC/
DEEPCOOL GAMMAXX GTE V2 CPU Air Cooler $29.99
https://www.newegg.com/team-16gb-288-pin-ddr4-sdram/p/N82E16820331354
Team T-FORCE VULCAN Z 16GB (2 x 8GB) DDR4 3200MHz CL16 $74.99
https://www.newegg.com/team-group-1tb-cx2/p/N82E16820331561
Team Group CX2 2.5" 1TB SATA III 3D NAND Internal SSD $88.99
Total: $589
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So if I get better fans for my sons pc will the performance and fps be better