cheapest option is probably a second hand office pc with a second hand 2-4 port 10gbit card in it
In the long run a PC will probably more expensive though, because it uses more electricity than a specialized embedded device. A specialized router is probably worth it if you stick with it for a while, at 10G there is little reason to upgrade.
Power is cheap as fuck where I live, ymmv I guess
Unless you go with a pc with 10gig interfaces my suggestion would be a mikrotik ccr2004-16g-2s and a couple of 10gig sfp+ interfaces. It comes with the added bonus of passive cooling and more software options than most of us knows what to do with. Even has WLC capabilities.
Do you want just 10Gb ports or do you also want 10Gb internet throughput?
A UDM-pro might be a good option in addition to some of the other suggestions here.
Check out things like "Protectli Vault" and just put pfsense/opnsense on it
Zyxel AX7501 has one sfp+ 10G wan and one rj45 10G lan port. Should be around 350$ if you can buy it where you live. I work at an ISP am that's the device we're giving to our customers for 10G.
In general I don't think you'll get much lower than that even if you build your own router.
Community for discussing enterprise networks and the ensuing chaos that comes after inheriting or building one.