The simple answer is...
There isn't one.
It's a question of what you want out of the system and the game.
I've seen at least one person in the bug reporting subforum for 2.2 complaining about graphical stuttering when his pc is based around a Core2Quad with 8Gb of DDR2 from 2007. Now (obviously) it wasn't playing the game well, but it was playing it. That system would be otperformed by even a bottom end i3 from the current generation, (it's also beaten by mine & that isn't exactly top of the line either).
Anyway, I digress, you should set yourself a budget of what you are willing to spend for the quality you want & work around that. I'll build (on paper) what I believe would be a decent low end PC that will play at 1080p reletively well.
Now bear in mind, this is the absolute bottom end that I believe should work fine, I am not going to put up an AMD based alternative (simply because there really isn't a future proof one) & for simplicity I'm also going to use only products that can be bought on Amazon.co.uk - there are other places to get them. I'm also going to assume you are not interested in overclocking & you have a monitor or tv to connect it to already.
The Processor:
Intel Core i3 6100 £92.91
Motherboard:
Gigabyte H110M-S2H Micro ATX motherboard £48.99
Memory:
HyperX Fury black series 8GB DDR4 £34.95
HD:
Toshiba 1TB P300 £39.99
PSU:
EVGA 600W PSU £47.95
GPU:
ASUS Strix GTX 960 £149.98
DVD/RW:
Liteon £12.17
PC Case:
CIT F3 Black Mid size tower £20.49
Total Cost £447.43 without an OS
(Windows 7 supports Skylake & OEM versions can be bought on Amazon for £35 or less).
Obviously there are some areas that could be saved, for example if you are upgrading from an older PC you may not have to buy a case, DVD drive, Hard drives etc - you may be able to recycle your old ones. That money that you save could be put towards a higher end i3 or low end i5 or a better GPU eg GTX 970 or GTX 1060. For a budget system however the list I've presented should work just fine at 1080p. It also allows you some wiggle room as far as upgrading goes it'll support everything up to top end i7's and DDR4 which is fast becoming the standard for memory.