I would argue that they’re actually not that much more expensive on a per-port basis within the same range.
Quite the opposite actually.
You stated unmanaged and a TP-Link SG-1008 is £40 on a large South American sounding website. The TP-Link SG-1016 is £52 from the same site and the SG-1024 is £80 from the same site. So three times the ports, double the money. Jumping up to the SG-1048 at £180 does increase cost on a per-port basis but you are paying for much more RAM, a bigger CPU and a pretty beefy power supply.
And it may be worth bearing in mind that a managed switch acts just like an unmanaged switch if you don’t use the management features.