Rbatson,
The kit new is almost 500 dollars.
The nitrous line would be extremely inexpensive and can be picked up at any auto performance store.... I would "guess" 10-30 dollars.
As far as how well it would work on your Cobra, how would you like an extra 50 to 60 hp at the rear wheels when you hit WOT?
It's a good kit that is as safe as N2O kits are going to get...
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"The Yellowjacket"
1998 Mustang GT
13.97@103
"Hey, you weren't supposed to be that fast!"- Turbo Eclipse Driver