There are actually many videos on computers built on a budget that are specifically targeted to run fortnite. You don't even need very recent hardware to run the game as it's easy on the requirements.
For a midrange system, if you want brand new parts you could even go with an 7th gen core i3 or 8th if your budget allows or Ryzen 3 paired with a 1050Ti or similar or even the new Ryzen 5 2400G if you're on a very tight budget as DDR4 RAMs are extremely expensive.
Searching on youtube for "cheap fornite PC" or "fortnite on a budget" will yield many results, I can point out a video from "TechYESCity" and another from "Jayztwocents" where one builds a PC using used parts and the later just builds one using a Ryzen 5 2400G.
But again, without knowing your budget, it's hard to give you a more precise answer. I also can give you pointers on how to put it together if you so need. Again, many videos geared towards more inexperienced or first time putting up a computer.