Case in point, I have a few recent-purchase machines with 2.5gbps networking but no 2.5gbps switch to connect them to because I personally can't justify their cost yet.
I suppose I could bond two 1gbps ports together, or something, but I like to think I have other yaks to shave right now.
https://www.amazon.com/5-Port-Multi-Gigabit-Unmanaged-Entert...
Personally I went with Mikrotik's 10gb switch but that needed SPF port thingies (which was fine for me, as I was connecting one old enterprise switch via fiber, direct copperering two servers, and using cabled cat7 or whatever for the Mac).
2.5gb is silly in my opinion unless it's literally "free" - you're often better with old 10gb equipment.
I think 2.5g is going to make it in the marketplace, because 2.5g switches are finally starting to come down in price, and 10g switches are roughly twice the price, and that might be for sfp+, so you'll likely need transceivers, unless you're close enough for DAC. (NIC prices are also pretty good now, as siblings noted. But if you go with used 10G, you can get good prices there too, I've got 4 dual 10G cards and paid between $25 and $35 shipped for each)
2.5gbps hardware need to come down to at least the $30 to $40 dollar range if they want to make any sense. Otherwise, they'll stay as niche hardware specifically for diehard enthusiasts or specific professionals only.
IMHO this is why Ethernet has stalled out at 1G. People still don't have large enough data needs to make it worthwhile. See also: the average storage capacity of new personal computers. It has been stuck around 1TB for ages. Hell, it went down for several years during the SSD transition.
It's really just the cost that's the problem, because paying 4x to 5x or even 6x times the cost of gigabit hardware for a 2.5x times performance boost doesn't make a lot of sense.
If 2.5gbps peripheral hardware costs would come down I will happily bet they will take off.
2.5gbps ethernet translates to roughly 250MB/s in real world transfer speeds, that's a lot. Literally over double real world gigabit transfer speeds, and far less likely to bottleneck you.