To build it I looked up part on the website Newegg.com, but also keep in mind the parts I list will be at retail price and Nintendo would actually buy them at wholesale price and I have to keep in mind that a profit need to be made from this as well. Finally the core parts will have to be modified to make a more dedicated system than a PC is otherwise I would not be able to get the full power of the parts.
Let's start off with the core components of the home console.$69.99 AMD Athlon X4 860K Kaveri Quad-Core 3.7 GHz Desktop Processor
$34.99 (after rebate) MSI GeForce GT 720, 1GB 64-Bit Graphics Card
$32.99 Klevv Fit 8GB (2 x 4GB) 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800)
$49.99 MSI A68HM-E33 V2 FM2+ AMD A68H 4 x SATA 6Gb/s USB 3.0 HDMI Micro ATX AMD Motherboard
$19.95 Seagate DB35 Series 7200.3 ST3320820SCE 320GB 7200 RPM 8MB Cache SATA 3.0Gb/s 3.5" Desktop Hard Drive
$10.08 LOGISYS Computer PS480D 480W ATX12V Power Supply
$17.99 (after rebate) XION Gaming Series XON-310_BK MicroATX Mid Tower Computer Case
Next I'll list other important parts but these one are not as specifice as above as they can be more easily switch with other parts.
$5 HDMI 4K
$16.19 PCI 8 Channel 8CH 7.1 Sound Card
$7 for a cartridge reader, this is the estimated cost I came up with based on the price of internal SD card readers. I went for a card reader instead of a disk drive because of the possible leak that the device won't have a disk drive.
$50 for one controller, either a Wii Motion Plus with Nunchuk or a Classic Controller.
This brings us to an amount of $314.17
You may have noticed that I didn't list an operating system, well since this is not for an actual PC it will not need the programs of such. Also I have no way of knowing just how much an operating system for a PC would be but I think it would be much less since video game consoles are dedicated systems and do not require the ability of a PC.
Next we got to figure out what we are going to sell are console at, and to do this I will look at the Wii U and 3DS. Keep in mind that these are estimates I found online.
$228 To build a Wii U selling at $299 https://filmgamesetc.com/2013/03/how-much-does-each-wii-u-console-cost-nintendo/
$101 To build a 3DS selling at #249 http://kotaku.com/5785605/so-how-much-does-it-cost-to-make-a-nintendo-3ds
So we are looking at an additional $70 to $150
Estimated retail total comes to $384 to $460
I must say again that the parts I listed are priced at retail and not whole sale that Nintendo would buy the parts at. So the price will be much less then what I just put down. So let's just do an estimate of $10 off most of the parts and say that comes to about $60 to $100 off the above total retail price.
This brings us to a final estimated cost for a 4K Nintendo console at retail to cost between
$284 to $400
Finally, for a PC the 4K Gaming may not work so well. I think it wouldn't even be possible to get a smooth 30fps on a PC. However a video game console is a more dedicated system which will allow the full use of the parts for gaming. With this in mind I believe a smooth 30fps would be easy, but 60fps is another story. Also I do not know how the games would look, how many particles it could render at once, how many polygons, how many physics it could handle. This is the stuff that I can not say.