I assume that is USD rather than Yen.
They were never much more than that new (always a budget effort) and if indeed people are generally opting for emulators, hypervisors and the like with newer devices then I can see someone pricing low to get rid of stock.
Never heard of nds-carts before, though I have not been paying attention to shops for a while.
As far as ttds/dstt family... even with the nice third party loader they were never that fun.
As a choice for super budget flash cart though then you could probably do worse and you can almost certainly experience a good chunk of the DS library with one running as well or better than stock if you don't use a SD card you found in a vintage phone.
Afraid I don't really have a good "get this" type suggestion for a DS flash cart to play all the games, maybe with some cheats. Such a thing could exist (technically speaking nothing is different with the higher priced offerings in any way that matters, all down the software) but seems to be lacking in the world. Hopefully one day.