I agree with CAP it is a lot of labor.
You MUST be sure the panels are very flat before even beginning this process. Every wave, dent, ding or hollow area will stand right out. You also face the inevitable sand-thurs of the finish in early stages.
The fact that it is fussy work, plan on having your speakers apart much longer than you think. Spraying polyester material is not for the faint of heart if you were thinking of doing it your self.
That said, if you are mechanical, have lots of patients and have no problems with DIY projects it is possible even if you have a body shop spray them and you do all the sanding and polishing.
Good luck with them feel free to ask questions if needed.