The $2500 quote was probably on painted stripes. There is no way that someone could charge that much for vinyl. And to answer your questions, Iv never heard of anyone clear coating their vinyl stripes. They will eventually fade out (anywhere between 3-5 years) depending on if you keep your car in a garage or outside. This is why I had to replace mine. And no they will not peel off in the sun. The ones I got are made by 3M and are super strong once the adhesive dries. Peeling them off is actually really difficult.
One problem I see with clear coating them is that you have to be extremely careful to clear coat only the stripes. If you will ever want to take them off, you probably won't be able to.
