The basic kit will include lifted coil springs for the front, drop brackets for the front axle beams, a drop Pitman arm for the steering, blocks for the rear springs, and 4 shocks. Options to consider adding are 2 more longer shocks if you have the quad-front on some Broncos, extended radius arms instead of drop brackets for the factory ones, and lifted spring packs for the rear. I think you will get a better deal ordering the kit online rather than your local 4-wheel drive shop. I have had good results with parts from Rocky Mountain Suspension. Some 4Wheel Parts Wholesalers stores are good, and some will rip you off. If you decide to have a shop install the kit for you, labor should run about $425-$450.
Keep in mind what your final goal is for the Bronco, too. A 6" suspension lift kit is nearly the same price as a 4", but you can run 35" tires instead of 33's on the 6". My plans are to race my 84 Bronco in mud drags, so I wanted the 35's. I know of several folks that have bought a 4" kit and wish they had gone with a 6" instead. If you just want a weekend trail rig for occaisional use, then a 4" with 33's will be better.