OK at first blush I think that's a crazy high price.
They are going to do what, clean the surface, lay the stripes in nice and tight and remove all bubbles, maybe give it a nice wax job over top, and send you on your way?
I got all windows except the front tinted, with them using their own materials and having to custom cut to fit, for just over a hundred. Can putting stripes on really be twice that hard, particularly since you are supplying the pre-cut stripes?
Checking my local chevy dealer for somethign similar; I find a decal/stripe package, we're talking five pieces, both sides, roof, hood, and rear, the stripes cost an amazing $300 but they will install them for $200 more. That's five pieces, for the price you're talking about, and it's at the dealer, which is never much of a bargain.
Unless these guys plan to ride on your hood and hold the stripes in place wherever you go, I'm thinking they are taking You for a ride.
Never had it done myself though, I have to admit; my idea of how to put stripes on my car involves some duck tape and an Xacto knife