Funnily enough I've been looking into this recently as well, considering a mix of 2.5Gbps and 10 Gbps to keep costs down - I have a server and two PC's I'd like to connect.

Going SFP+ to RJ45 gets rather expensive, so I was considering a more expensive switch in the first place, but these don't have as many 10Gbps ports, but would allow me to run 1 x 10Gbps with 2 x 2.5Gbps with the future option of 2 x 10Gbps and 1 x 5Gbps if going for the Netgear switches below.

Switches I have on my list so far.

£138 ZyXel XGS1010-12 8 x 1Gb, 2 x 2.5Gb and 2 x 10Gb SFP+ unmanaged

£188 Zyxel XGS1210-12 8 x 1Gb, 2 x 2.5Gb and 2 x 10Gb SFP+ Managed

£208 Netgear MS510TX 4 x 1G, 2 x 1G/2.5G, 2 x 1G/2.5G/5G, 1 x 1G/2.5G/5G/10G, 1 SFP+ 10G Managed

£302 MS510TXPP-100EUS As above but with POE+

For connection to the sever (which is next to the switch) I'm considering going with

SFP + DAC cable, and an

SFP+ card. Both my PC's are on CAT5e, cables are 12 & 13 meters long so should be good for 10Gbps, but will likely run 2.5Gbps to start with.

So I'll be very interested in what suggestion others have as well.

ETA. That card I linked to on eBay is a fake

https://sviko.com/t/how-to-distinguish-10-gigabit-network-card-intel-x520-da2-from-chinese-fakes/37