1997 Ninja 250 Spark Plug Heli-Coil?

So yesterday as I was driving my Ninja 250 (1997, 26k kilometers), and I blew out my right spark plug. I walked the bike home, and with some help from my dad's mechanically inclined friends, we determined that the spark plug "housing" was stripped. Heli-Coil was the first fix to come up, so we are planning to get 2 new spark plugs, and Heli-Coil the inside (take the head off, the holes are REALLY deep on this bike.) There is one problem though. Apparently the engine is aluminum, and Heli-Coils are Steel. Different expansion points could cause problems right? Is there any alternatives to Heli-Coils? What is the price range on these? Any tips on doing this? Thanks in advance!