Ok
You want to try muzzleloading, so your first choice is not only a matchlock, but an obscure 16th century Asian one?
You are unwilling to pay $900 for a functional reproduction of said obscure Asian matchlock?
You rarely see other muzzleloaders for over $400?
I applaud your obvious love of history and desire for a unique historical arm. And of course I respect anybody who wants to burn any powder of any kind.
I would suggest a little more research into muzzleloading firearms both historical and the modern reproductions/interpretations that are available for purchase. As you can see by the dearth of available tanagashimas these are not a commercially produced item, nor are most faithfully historical reproductions of arms of that period.
Most likely you would have to build this yourself or find someone who willing to do it for you. No idea where you'd find plans for one, but I wouldn't be surprised if they are out there. $900 would likely be enough for the parts for this project but not the labor. Some of the parts would likely have to be modified parts borrowed from other guns.
If you are dead set on starting with a matchlock, and don't want to build one yourself, or have one built, look for a used matchlock made by Leonard Day or others that sometimes become available. If you're patient and keep looking they do turn up. You will pay a lot more than $400 for one.
If you're seeing muzzleloaders for ~$400, you're looking at stuff made in India and perhaps that's where you should look if you just want a cheap shootable historical looking muzzleloader. I've never owned one of them so maybe someone who has will come along and discuss that option.
Good luck and do not get discouraged, your first muzzleloader will likely be 360 degrees off what you thought you wanted when you start to learn a bit more. Lurk around some of the dedicated muzzleloader forums out there, they have people there who's sole hobby is matchlocks and pre 18th century firearms, and lots of information.