Having the Big East TV markets and a soon to be new Big East Network totally outweighs the costs. Especially since anything but a rebuilt Big 12 is just about as distant as joining the Big East.
I'll go out on a limb here and say the Big East has a brighter future than the Big 10. If the 4 b12 remains join the Big East and they start a new network with equal revenue sharing and no outright controlling power of a school the Big East will thrive.
The Big 10 at that point would be surrounded by the Big East (who would now have no incentive to leave because they also have a cash cow network and have larger markets). The same goes for worrying about schools being poached by the ACC/SEC. If the Big East has it's own market and revenue sharing they don't have a big draw to the BE schools.
The new Pac 10/Big 12 South combination would have a decent TV footprint, but would be far to expansive geographically to work very well to function. They will break up eventually just like the old WAC, or will continue by being dominated by the 'power' schools like Texas, OU, and USC. See the Big 12 for how that worked out.
The SEC and ACC may merge, and that would be the only comparable conference, but I think the new Big East would have a much better academic fit for ISU than that would.
I know that was long winded, I'm just very convinced there is no better fit for ISU than the Big East. EVEN IF the big 12 were rebuilt.