So in the pursuit of diversifying my gun collection, I decided I wanted to try a muzzle loader. I've been looking for a tanegashima, but the cheapest functional one I've found is $900, which is far more than I'd like to pay for a muzzle loader. Other MLs I've seen are rarely above $400. Does anyone make an inexpensive reproduction or is this something people would generally make themselves? I have spent many hours on google, and had no luck.

Thanks

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.

He's probably seeing T/C Hawkens on the high end and CVA it such on the lower end.

OP I want to have a bespoken Carolina pattern smoothbore 20 bore authentic to late 1700s militia service in my area. If it could be had for $900 I would have pics posted by now.
You can't compare prices of mass produced low end guns to the type of work and materials you look for.

Dixie Gun Works used to sell a reasonably good Tanegashima matchlock repro about 20 years ago, about a 20 gauge or so. They turn up on gunbroker.com every now and then. I've handled them, they're all right.

I'd stay way from India-made repros, though. Good for firearm-clueless reenactors, not good for years of live firing.

DON'T fire an original.