Here are my thoughts. First, though you CAN use a dry kit on a stang:
DRY N02:
Pros - Avoids pooling of fuel and potential backfire. Lots of interesting technology. Some systems will read your 02 sensors for A/F and adjust accordingly and others can determine exactly how much nitrous you are adding and add the appropriate amount of fuel. There are many safe dry kits that have sound theory behind them. Most are very effective with stock fuel systems up to 125 shot.
Cons - Kits can be complicated to install. They involve too many sensors and inputs. Systems that read 02 sensors don't have any way of knowing what is going on at each indivdual fuel injector. Kits are "conservative" as they continuosly make adjustments, therefore, a 100 wet shot will net you more hp than a 100 shot dry kit.
WET N02:
Pros - Simple and effective. Biggest possible bang for the buck. Can be very safe if all the appropriate safety devices are used (window switch, fuel regulator etc...)
Cons - Pooling of fuel resulting in backfires (avoidable if window switch is used).
If I were to go with a nitrous kit, I would probably use NX EFI Wet, 100 shot, with all the appropriate safety devices minus the remote bottle opener.
Either way, figure to spend (for new) $400 to $1500 max. You can get a really nice, effective, safe system for $1,000.
Nitrous is not very streetable, though. Great for racing, but you really should have a "flip-chip" with a nitrous tune that you can switch back and forth between especially is using on the street.
Also, the juice cost money. A 10 lb bottle might get you 8 - 10 blasts, that's about $3.00 per use. A supercharger or turbo is much more streetable and most likely cheaper in the long run with less worries.
But, there is a certain thrill beghind no2 that a blower does not afford.