You really need only the Press N Snap tool and the button and socket dies that come in the kit. Perfectfit has the tool and 4 piece die set for $112, and that's about as cheap as you'll find. http://www.perfectfit.com/15336/1544...Snap-Tool.html
There are dies for Durable Baby Dot fasteners, but unless you use a lot of snap fasteners they are not necessary. Then you will need caps, sockets, studs, and eyelets. Make sure you get both nickel over brass and stainless versions. You can add other things later.