There is a lot of talk in this thread about using 10GbE at home.
The consumer/prosumer RJ45 "new" 10GbE hardware is currently very expensive.
If you want to use 10GbE at home, e.g. a NAS and a few machines,
If you do not want to wait for prices to go down in 5 years,
If you do not want to sell your Grand-Ma but spend as low as possible,
If you know what you are doing:
Go with SFP+ used/open box/new hardware from eBay.
For the cards, there is a palette-size load of SolarFlare cards at around $20. See
https://www.ebay.com/sch/i.html?_fr...olarflare+10gbe+sfp&_blrs=spell_check&_sop=15
You need a free PCIe Gen 3 x8 lanes, maybe x4 lanes depending on the model you select, so you'll usually insert the card in the 2nd PCIe x16 lanes slot on regular desktop PCs. There is nothing preventing you to use the 1st x16 lanes slot for the NIC and the 2nd for the graphics card if it makes the motherboard happier.
You do NOT need a switch if you only have one PC and a NAS or a server such as ProxMox or just a 2nd PC. Just directly connect the 2 machines with one cable and set your NICs up manually with fixed IP addresses. If you choose a dual port card, your PC can talk 10GbE to two other machines.
For the switch (if necessary), search for "switch 10GbE SFP" and filter on "10 Gigabit Ethernet", from time to time you'll find models such as:
https://www.ebay.com/itm/314318172336
So I strongly suggest that you browse eBay offers regularly until you find a cheap one. Be patient.
If your PC already has an onboard 10GbE NIC, usually an Aquantia chipset, you'll need a 10GBase-T SFP+ Transceiver RJ-45 SFP+ (e.g.
https://www.ebay.com/itm/234685127893) to connect it to an SFP+ switch. Usually $45/$50.
While using an unmanaged switch, you still need to set your NICs up manually with fixed IP addresses. Unless you know what you are doing and have a DHCP server on the 10GbE subnet. One of your machines, using Linux can become the router between your 10GbE subnet and your usual 1 or 2.5GbE. The setup is not rocket science.
For the cables, just dig into this:
https://www.ebay.com/sch/i.html?_fr...0&_odkw=10gbe+SFP+DAC+cable&_osacat=0&_sop=15. $10 to $50 depending on length (<1m to 10m). If you need very long cables, you will have to go optical with SFP+ transceivers and AOC cables. Costs more.
Note: not all the 10GbE SFP+ cables are the same, avoid the ones saying Cisco. I tried one, it did not work with my Microtik switch. Then I tried one that did not mention Cisco and it worked AOK.
FINAL NOTE
Used 10Gbe SFP+ cards and switches are continuously appearing on eBay. They come for data centers that dropped 10GbE entirely. The hardware was designed years before the 2.5GbE and 5GbE standard were written. These cards and switches will NOT auto-negotiate for 2.5GbE and 5GbE (thus you setup a Linux router to link the two subnets).
Do your home work. Visit the product pages to get the specifications and buy cards, switches and cables that work together.
To add 2.5 GbE for cheap to a motherboard that do not have an onboard 2.5 GbE chipset:
Solution #1: go with a USB 2.5GbE adapter. The most commons use a RTL8156B Realtek chipset. You can find them by looking for "RTL8156B" on eBay. Usually around $20. Just make sure the seller says RTL8156B with the "B" at the end. The original RTL8156 was let's say painfully inadequate (read "not working"). See
https://www.ebay.com/sch/i.html?_fr..._odkw=RTL8125B&_osacat=0&_sop=15&LH_PrefLoc=2
Solution #2: go with a PCIe card. The most commons use a RTL8125B Realtek chipset. Convenient if you have a free PCIe Gen 3 x1 lane slot, or above. Usually around $20. Make sure again the seller says RTL8125B with the "B" at the end. The original RTL8125 was yada yada yada. See
https://www.ebay.com/sch/i.html?_fr..._odkw=RTL8156B&_osacat=0&_sop=15&LH_PrefLoc=2.
5GbE?
Avoid the USB 5gbE adapters like the plague. Most of them use the same USB 3.0 chipset to bridge USB to Ethernet. This USB 3.0 chipset is Gen 1, meaning max theoretical speed 5Gbps. So as you may surmise, tunneling 5GbE Ethernet inside 5Gbps USB is going to be a showstopper. The max speed you'll get with these USB 5gbE adapters is about 3.5GbE, not the expected 4.5GbE. This being said, if you're happy gaining one more Gigabit compared to 2.5GbE, why not. But that will cost you around $80 per adapter. At that price, it makes more sense in terms of value to jump directly to 10GbE.
My guess is that the manufacturers will just loop with initial high prices for 2.5GbE, then for 5GbE and then for 10GbE. Each time presenting it as the "New New thing Best of the Best" while 10GbE has been used for 2+ decades in data centers.