I did find ads for replacement back panels with a new plastic or glass window but those were also relatively expensive.
Miata door window replacement.
This is a typical miata door assembly.
Note that not all miata s will have the same door panel some earlier models may not have the.
A catalog sells replacement plastic back panels for 170 and glass back panels.
This repair is performed on a 1992 miatain the photographs and example below.
Use white lithium grease.
Mazda sells a replacement back window for 370 and that is just for the clear plastic part you then need to take it to a shop to have it installed.
Later models may require a different method.
Any of these problems the same door and window disassembly is required.
Lubricating miata door windows lubricating the door window channels can make the windows roll up and down more easily and can prevent future problems with the mechanism or cable.
The inner panel shown is for a miata with manual windows.
It may not be necessary to remove the door panel to do an adequate job.
The original parts get cracked rusty and unsightly so replace the belt line molding on your miata for a refreshed factory look.