Ubiquiti has recently launched an upgraded version of the Flex Mini Switch, now with four 2.5GbE ports. This little switch is only marginally more than the standard Flex Mini, priced at $49 in the US. For comparison the 1GbE version is $29. According to some early users, the new 2.5G version also has support for proper VLAN management within UniFi, whereas with the old version couldn't have custom port profiles which did restrict its usability somewhat.
Just like the 1G version, the 2.5G can be powered up via USB-C or PoE (802.3af)
The new Flex Mini 2.5G is listed on the official Ubiquiti Store in the US for $49, but at the time of publishing it is out of stock. In the UK, it is listed as "coming soon" and is priced at £46.80.