$50 seems a bit high in my opinion. $30 is the ballpark I was thinking where the value proposition over a dongle makes sense.
As far as @mrwm’s concerns about selling/promoting on the community forum, I think that quote is slightly out of context. Nirav was responding to someone reselling their Framework laptop. Other threads (like the SNACK drawer) have been fine. This is the expansion cards forum after all 
.
Maybe another option is Tindie or a DIY kit model? Print a bunch of PCBs and sell those with a schematic and BoM so buyers can save money on components if they want.
Maybe I’m just weird, but I would be more willing to buy a kit that I can consider a project for a higher price. Dirt cheap consumer electronics have made it hard for me to overcome the psychological hurdle of expensive pre-assembled niche devices. Though, if the board only has microscopic SMD components, then maybe DIY assembly isn’t achievable.