Amazon has the TP-Link Gigabit Ethernet Media Converter (MC220L) for $20 with free shipping on $25+ or with Prime. List price: $25. Features works with both single-mode and multi-mode fiber SFP modules, 1 Gigabit SFP port, 1 Gigabit RJ45 ethernet port, power/link / transmit LED indicators, 802.3ab/z/x network standards.
Has excellent Amazon Reviews.
Amazon has the ARRIS Surfboard G34 DOCSIS 3.1 Gigabit Cable Modem & Wi-Fi 6 Router for $198 with free shipping. Works with Cox, Spectrum, Xfinity and other cable providers. Not compatible with DSL or Fiber internet providers.
Has above average Amazon Reviews.