You're paying for the time and assembly and configuration work really
This thing actually reads optical discs from different systems, which is not something I've seen before. So, that's more than time, assembly and configuration, in that this is something new (to me, at least) above even a PC. As far as I know, I can't insert a Sega CD into a PC and emulate it off the disc. (or can I?)
Also, we have three families here:
* Do it yourself products as this AtariAge commenter suggests and play ROMS you unearthed on the internet
* Buy one of these retro unit consoles from hobbyist groups like this Seedi, that can play legitimate game media (and ROMS)
* Buy one of these retro units from a larger company, like Nintendo, often with a limited but legal game selection
We've seen lots of the middle tier - hobbyist (or small company) products from companies like Hyperkin (using both hardware and software emulation) and this crowdfunded start ups. These are the ones the commenter is saying we are paying for time, assembly and configuration. I think there is a bit more here. The configuration may not be trivial, in that they should have chosen components (or designed some unique ones) and designed a unit eith an expert eye toward things like adequate cooling and performance. Assembly is not always easy either, as someone who has failed to complete a few mods in his day. There is also a need for quality checking the assembly and redressing flaws that are found - that's a big plus.
While the commenter may have included OS in 'configuration', that's not trivial either. They need to build a user friendly operating system requiring minimal learning across a range of technical skill sets, and put it all together in some eye pleasing way. For this Seedi thing, there are controllers involved too. They may also need to select and acquire rights to a set of programs to help sell the product. Then there are rounds of testing, possibly with minor redesigns and firmware updates as well.
I'm glad we have this middle tier.