I thought your car already had a non-airbag wheel...?
Anyhow... going on BR's advice, I got the Daikei hub and it was money well spent. It's absolutely plug 'n' play. However, if you search Miata.net I think you'll find some writeups in the Garage section that will tell you how to fix the flashing airbag light with resistors and soldering and other technical monkey business. I'm just not that smart...
I think R-Speed carries the Daikei hub for about $130... maybe? I got mine from some place that's out of business now.