These are well-engineered, real-world performance springs that are great for dual-purpose street and autocross/lapday use. I had these on my 2001 Miata for about 10k miles, and they're in great condition. These are $249 new - read up about them on the Flyin' Miata website:
http://www.flyinmiata.com/index.php?dep ... %201990-97
A lot of the lowering springs out there reduce the suspension travel too much without a corresponding spring rate increase, which means you're banging the bumpstops when the suspension in loaded up. Stock Miatas are pretty softly sprung from the factory and even have a tendency to do this in aggressive driving, as well. The Flyin' Miata springs have no squeaks, rattles, or other headaches like the cheap stuff, and the ride quality is pretty tolerable for the increase in spring rate. Pair these with a good set of dampers like Koni Sports, Bilsteins (like these), or Tokico Illuminas, and you'll have a fun, very competent suspension setup.
Spring rate comparison (lb/in):
Flyin Miata - Front: 318 / Rear: 233
Tein S-Tech - Front: 235 / Rear: 173
Racing Beat - Front: 207 / Rear: 145
Eibach Pro-Kit - Front: 140 / Rear: 120
Pictures of the goods:
What it looked like on my car. I just took them off to run in Street/stock category.
I will be the Street Survival event on Saturday, as well as the OMRSCCA RallyCross on November 11 if those work for you.