How much for a Skylake-based system? Very rough and ready component selection from MSY and PC Case Gear.

CPU	i5 6600 (modest)	325
CPU	i7 6700K (one-off cost for ongoing performance)	519
Mobo	Asus H170-PLUS	169 (H170 PRO GAMING would be a solid choice too, at $230)
RAM	16gb of DDR4 2400MHz or whatever	150
SSD	Samsung 850 EVO M.2 120G/250G/500G	99 / 135 / 243
Case	Antec P280	169
PSU	whatever	100
OS	Windows 10	???

If you want to cheap out a bit, you can tweak a few little things:

Select a basic H170-based motherboard: Gigabyte or ASrock will be somewhat cheaper, but it still bottoms out around $150. The cheap Asus H170 board is $160 and it uses DDR3 RAM (widespread, cheap, will become "old" in ~2yrs)
Use DDR3 RAM: it's cheaper and still very performant, just not future-proof. You can get 16gb of DDR3 for $115 at MSY, but will need to buy a mobo that takes it
Use slower RAM: Baseline DDR4 RAM is 2133MHz speed, very slightly cheaper at about $140 from MSY
SSD: you can cheap out a bit with a different brand SSD and maybe save $20
Case: the P280 is a fancy noise-dampened case. You can pick a basic one and maybe halve the cost

Choice of CPU

Current socket is LGA-1151.

April 2016

What I actually bought from MSY:

CPU	i7-6700K	484
HSF	Noctua NH-U12S	89
Mobo	Asus H170M-PLUS	165 (H170 PRO GAMING would be a solid choice too, at $214)
RAM	16gb of DDR4-2133 Corsair Vengeance LPX 2x8gb kit (13-15-15-28)	103
SSD	Samsung 950 Pro M.2 256G (MZ-VKV256)	239
Case	Fractal Design Define R5	165
PSU	Antec Truepower Classic 650W TP-650C	135
OS	Windows 10 Home/Pro	137

Using my existing GPU, that's a total of $1517.