K&N 57i Induction Kits for Miata fit Pro...
 

I found this while searching on K&N website:
http://www.knfilters.com/images/57i/57-0299.jpg
K&N 57i Induction Kits for Miata(57-0348 94-98, 57-0434 99-01):

http://www.knfilterchargers.com/search/appsearch.aspx

For installation and pics(57-0348):
http://www.knfilters.com/57i/57-0348%2017292.pdf

Looks like it would fit our Pro and might be cheaper.
All you need with that is custom 2.5" pipings later on. It could be a good start for a custom project.:D

hmmm...that PDF file is fucked up on my comp