Located to our south in Iowa is the Hot Rods company, home of Hot Cams, Hot Rods, Pivot Works, and affiliated with Vertex Pistons. (Please see
http://www.hotrodsproducts.com/.)
This company has done pretty well, and if there were enough demand for GasGas pistons, my guess is that Vertex Pistons would be made available to us.
I, for one, am with Glenn. If you toast a piston skirt, it can do a lot of damage (think cases). $200 for a piston kit isn't a bad deal, really. It's cheap insurance. If you change it at 100 hours, it cost you $2/hour. You're burning through way more gas than that. Where else can you have fun like this for $2/hour?
Fuel:Oil mix has quite a bit to do with ring and piston surface wear, but not much to do with fatigue life. If you run your bike hard and don't change a piston, you'll break one. That $200 piston looks cheap when compared to the other result.