sorry for late input. my wife had a miata, i tore that little car up, fun. i got her a hard top...easy to install, we could place it on the side of the house if she wanted to have the top down or the soft top up. i don't know what year your car is, but used miata hard tops should run around $500.00 and up, maybe can get one to match your car's color, but if not, should not cost over $120.00 to paint one.
but, if staying with a soft replacement, and you plan on keeping the car for more than another year, i'd also say canvas with glass, the plastic windows fade and crack in the sun, and no telling how long one will last if it's made by a third party (not a Mazda oem part/build).
2 cents worth.
