Either of you two look at what a Mac Mini is? ://.apple/mac-mini/
I doubt he can find a GPU to fit.
It’s a Mac with integrated graphics. He’s lucky it even opens Unreal, IMO. The CPU is below recommended spec as well.
The thing is, if you can work with your situation long enough to package and release a game, it will run fine for anyone above minimum spec. The Unreal Engine runs a bit slower in development mode than it does in shipping mode. A shipping build also trims out a lot of the code you won’t need (like the editor).
Sad to say, if you’d spent that $500 on a prebuilt tower, you could just buy a new graphics card for it. Instead, you’re looking at a new machine.