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