The only remote competitor to the NeoSD, the Darksoft Multicart, is/was slightly more expensive than the NeoSD. Do you really think that if Terraonion overpriced their product, Darksoft wouldn't use that and price their product competitively lower? Nope, they would make a loss on their products. This is simply a result of the cost of R&D, especially when it comes to FPGA programming and reverse engineering Neo Geo carts, which are much more complex than ye olde MegaDrive's carts. Your whole "the parts aren't that expensive" tirade leads to nothing, if this was the case with everything we bought, we'd be spending a hell of a lot less on electronics and other products, but we're not as R&D and marketing do cut into profits, especially with something as niche as Neo Geo.
That niche-ness also adds much more research time, because the Neo Geo simply is less documented technically-wise than say, the SNES (as you mentioned Analogue NT), simply because the SNES has way more interest due to the fact way more people grew up with an SNES in their house than a Neo Geo, so only rich kids and avid arcade fans got exposed to the NG. Thus, less interest means less development, which means less documentation, and that in turn results in more research and more costs.
The Chinaman multicarts are cheap, because they hacked it up in the cheapest way possible, omitting FPGAs and using significantly lower quality components in order to cost and R&D cut to the extreme, which results in glitchy games, and essential games missing because they can't get them to work at all. That, and with China having fewer employee's rights, they can probably significantly underpay employees, which also helps, something Western companies making these carts can't, and shouldn't of course. That combined does end up in a $60 product, but one that isn't going to get you all the Neo Geo favorites, or games that run 100% as intended. It's like buying a $60 smartphone, it'll work, but not very well. Does that make all $200+ smartphones overpriced? It would be in your argument.