I was thinking about making a custom mp3 holder that would go in place of the ashtray for my SA. What do you guys think? How hard would it be? Also any pointers on how I should start this?

Something like this crude paint drawling. It would fit just like the factory ashtray no modifications.

 

better idea:

pull the ashtray out and then ditch it. buy a set of cup holders for a 90-97 miata. this is go straight in place of the ashtry, direct swap. after that get some foam like whats used in protective carrying cases. cut it to fit into one of the cup holders. after that cut it so your mp3 player will slide in nice and snug.

now you have cup holders and a secure way to hold you mp3 player.