Buy the Timesert kit for around $200 and do it yourself, or have Ford do it. Unless you have a really good mechanic that you trust, and will do exactly what you want. Most mechanics shops that don't specialize in Mustangs will try to just put a helicoil in there, which is not a permanent fix, and will eventually blow out as well or come out with the sparkplug on the next plug change.
I know $200 sounds like a lot, but if one plug has blown out, chances are you'll lose a few more over time. You can get really good at doing them after the first one, and fix others in less than an hour. The first one, you'll just be nervous that you're going to screw up, but after that one you'll realize it's a piece of cake.
From your past posts, it sounds like you're a pretty competent guy with a car, I don't think you'll have a single problem with this one. Just use a lot of grease on the cutting tool to catch the aluminum shavings, use or make a small tube style sucker for a vacuum (I stole a piece from my wife's Kirby set), and suck out any extra, and then blow it out really well with compressed air to make sure you get any stray shavings out. Using a lot of grease and changing it on the tool often, I had very very few in the cylinder.
2001 Dark Highland Green Bullitt [email protected] naturally aspirated on a bone stock 2V longblock
Under Reconstruction for RS275 Drag Radial Class Pushrods and Powerglide Coming Soon If it weren't for physics and law enforcement, I'd be unstoppable.