It looks like the Sniper kit goes for around $420. However, that is only about half of what you need.
You will need a window switch, a blow down tube, purge kit and bottle warmer.
Like I also mentioned, the Nitrous Outlet kit is specifally designed for the 3.7 Mustang. So all of the wiring, mounting points, etc, will be exact. With the NOS kit, you will have to figure all that stuff out yourself.
The Nitrous Outlet kit also uses a plate instead of a nozzle. The plate systems tend to produce better results as it atomizes the nitrous and fuel better than the nozzle systems.
Also, nozzle systems are more likely to cause fuel puddling in the intake, usually resulting in the upper intake and hood being blown off the car. This is the result of the fuel not being atomized well enough.
It's your money, buy what you want. I however, will be spending my money on the setup I listed.
99 Chevrolet Camaro Z28 M6 - 6.676 @ 103 in 1/8, 10.512 @ 130.2 on street tires, H/C/I
93 Eagle Talon TSI AWD 5spd - Built 6 Bolt, 16G Evo3, HKS 272 Cams - under construction