Can this head still be used?
 

Can it be used? And what would you pay? It was supercharged and ate a small piece of piston.

99 head.

Thanks.

The best answer is a caveated "it depends".
1. Did the valves, seats, or guides on that cylinder suffer any damage when meeting the departed piston??
2. How well do you want the damaged combustion chamber repaired?? (You can't leave the rough damaged edges, they can cause hot spots and detonation. If you have them ground smooth, the volume of that chamber will be larger than all the others and that cylinder will have slightly lower compression. Paying a cylinder head shop to fix the chamber back to stock size may cost more than the head is worth.
3. Is the head surface within Mazda specs? Have you checked for warping?
4. What is the condition of the cam journals and caps in the head?

If it was me, I'd want a pretty substantial discount to buy that head; YMMV.