If its your first SAS, and you have to ask Qs like that, I say get the kit. And you still need other thing that are not included in the kit: 2 off the top of my head are gears and a drive shaft.
There are other things you can do to make is less expensive, such as running rear springs up front, making your own brackets etc.
Ive seen them done for free, Ive seen them cost as much as 3k. It all depends on your skill level and dedication.
Ill be going 3link next winter on my TR, estimated cost is about 2k.
What kit are you looking at? TG?
You get what you pay for.