wireless nas with usb drive

I'm looking for wireless nas to which I could connect external usb drive(s).

If such a device could come without any internal drive (only ports for external usb drives), that could be even better! Or if it has one, it does have to be large in capacity.

I looking for such a device because I don't want the storage to be attached (wired) to a router or a computer, and I might need to (cold-)swap the drives.

Ideal price range would be around $200 or less, depending of the internal storage.

If you have any recommendation, let me know!

Thanks.