Thanks for considering Rotary Resurrection for service for your RX-8. I have tried to be involved in the 8 community in the past 4-5 years. I can offer rebuilds for the Renesis powerplant should the need arise, and have set about the task of obtaining renesis cores and used components in the last few years.
Most all of these vehicles have now come out of dealer warranty, so I have now moved into repairing RX-8's consistently, having performed tens of rebuild and installation jobs at this point. I am familiar with the common issues on these specific cars and can give you a good idea what to expect that your car may need.
Should the need arise to seek a replacement engine somewhere other than mazda (under warranty), I can almost guarantee that my rates would be far less than that of mazda or any other high end rotary shop for the same service. Nevertheless, expect the cost to rebuild your blown renesis to be significantly higher than that of the older rotaries. In those older engines, apex seal breakage usually meant that you needed a replacement used rotor and rotor housing to make the engine whole again. Due to the new design, when a renesis actually breaks apex seals, not only does it still destroy the rotor and rotor housing, but since there is no peripheral exhaust port for the seal fragments to exit, they get thrown around inside until they find their way into an intake or exhaust side port. In the process, they wedge between the rotor and port closing edge, damaging the adjacent iron housings as well. This extra damage (4 of the 8 major parts in the engine) coupled with the fact that renesis cores are hard to come by and new parts are expensive, will make the rebuild costs considerably higher than what we are accustomed to.