Instead of buying run flats why not use slime.

http://www.slime.com/

Here is the required warning,

WARNING: For high speed application (over 65 mph) use only as a repair - may cause excessive vibration when installed in front tires - to ensure safety, have treated tire inspected by qualified tire professional as soon as possible after puncture occurs. Slime will not seal sidewall punctures and should not be used with faulty valves or damaged rims.

I haven't used this in a car or truck tire, but i have used it for many other applications and it works great.