Honestly, I'd highly recommend building one yourself if you're up to it. I did it for the first time myself last year and it was incredibly easy. Got an I3 6100, Gigabyte LGA1151 socket motherboard, 8 GB DDR 4 Ram and a 500 watt PSU and it came to a total of £248. I'll be switching out my GPU to a 4 GB RX 470 aswell (between £169-£200). You can get some really cracking value video cards. For example an AMD RX 460 2GB DDR5 only costs from £89.99, or you can get an Nvidia GTX 1050ti from £135 on Amazon (variable deals online). Both cards are solid so can build from there depending on what other games you play, or do with your desktop, and you can play games 1080p.
It's really really easy (and cheap) to make your own desktop with so many easy to follow guides on youtube. The problem with pre-builts is you can be ripped off by what stores call "gaming rigs" and they turn out to be anything but. And they'll be loaded with bloatware. I also recommend checking out Reddit-there's a lot of really useful advice on various budget/mid range/high end builds.
