There are no longer any cheap parts…
Power Supply: I like modular power supplies with good length cables and good connectors. EVGA Supernova, Seasonic …dozens of brands very expensive but maybe a deal on eBay. If you are going to be mining with several GPU’s you may need two smaller or one bigger power supply. Two 850 Watt power supplies are good, and I suggest the 1300 G3 or G2 but they are expensive…Here’s a sample:
EVGA - GP Series SuperNOVA 1000W ATX 80 Plus Gold Fully Modular Power Supply … 843368048617 | eBay
Used - Very Good: BIOSTAR TB250-BTC PRO LGA 1151 12 GPU SUPPORT ETH ZEC 3 YEAR WARRANTY - Newegg.com
Mining motherboards are selling for several hundred dollars now. The B250 is my favorite but the H110 works nearly as well. They can run on GB or RAM and require 6th or 7th gen cpu’s like this Celeron:
Intel Celeron G3930 Kaby Lake Dual-Core 2.9 GHz LGA 1151 51W BX80677G3930 Desktop Processor Intel HD Graphics 610 - Newegg.com
or this I3 Pentium Processor:
Intel Core i3-7100 Kaby Lake Dual-Core 3.9 GHz LGA 1151 51W BX80677I37100 Desktop Processor Intel HD Graphics 630 - Newegg.com
Try to get a cpu with the fan. The I3 is 2 core / 4 thread while the Celeron is only 2 core / 2 thread. It doesn’t take much horsepower to mine with GPU’s. But these motherboards require the 1151 models that are NON 300-series which means 6th or 7th gen cpu’s.
Memory: DDR4 - 2400
CORSAIR Vengeance LPX 8GB 288-Pin DDR4 SDRAM DDR4 2400 (PC4 19200) Desktop Memory Model CMK8GX4M1A2400C16 - Newegg.com
Frames: This is where you lay out all your supplies to start mining. The price and availability of frames has sky-rocketed recently but I prefer the 6 or 8 GPU VEDDHA style frames. You can also purchase the 2020 extruded aluminum rods cheaper and make the frame yourself. Here are samples:
6 GPU Stackable Mining Case Rig Aluminum Open Air Frame For Ethereum ETH ETC BTC | eBay
8 GPU Stackable Open Air Mining Case Computer Frame Rig Ethereum ETH Bracket | eBay
Build your own:
ZYLtech 2020 Aluminum T-Slot Aluminum Extrusion - Black 2000mm CNC 3D Printer | eBay
You will need 90 degree mounts and M3, M4, M5 screws of about 8mm length or more plus drop in nuts for each size. But the aluminum can be cut with a hacksaw easily.
Boot Drive: You need a boot drive or SSD to run the OS. You can download the mining software onto it as well. Software is available on GitHub, just Google it for the name, like Phoenix Miner, or search by the coin … say ETH. Here’s a sample since these motherboards don’t have M.2 connectors.
Silicon Power Ace A55 2.5" 128GB SATA III 3D TLC Internal Solid State Drive (SSD) SU128GBSS3A55S25AE - Newegg.com
This will get your started, and you will need to learn other mining methods and Operating Sytems such as NIcehash, SMOS, HiveOS, where you can simply set up your entire rig and operating parameters.
I could point you to several videos, but you must learn to DYOR (Do your own research).
Without those super OS’s and just using a miner, wallet, and pool, you’ll need to control your video cards with programs such as MSI afterburner or X1.