As far as steps, the above posters have pretty much called it. It's a very easy swap, just remove your current intake and replace it with the Six Barrel intake and start bolting on the pieces to complete it, it's pretty straight forward. As mentioned, if you buy new reproductions they tend to come out of the box on the lean side so be aware of that once you start adjusting your base settings.

I'd highly reccomend that you put a sharp tune on your car before starting the swap to eliminate non carburetor related gremlins when you do the swap, set your timing, check your vaccuum, make sure all of your other ignition componants are in good working order, etc. The last thing you want to do is chase your tail when tuning your six pack (which is not that difficult BTW).

As far as cost, it varies. I'd suggest making a shopping list and having a look around the internet, right here on Moparts is a good place to start, allot of vendors advertise here as well as other members selling new or used parts they no longer need, and of course ebay is a good place to shop as well.

Basic shopping list for a stock setup:

Intake manifold
Intake gasket set
Carburetors
Progressive carburetor linkage
Fuel lines
Vaccuum hose w/T-fitting
Carburetors
Carb base gaskets
Carb air cleaner gaskets
Carb air cleaner studs & wing nuts
Carb hold down bolts
Throttle cable
Throttle cable bracket
Throttle return spring bracket
Throttle return spring set
Coil braket
Idle stop solenoid
Throttle stud & nut
Automatic choke assembly
Air cleaner base
Air cleaner lid
Appropriate valve cover breather package for year of car

*Picture below shows a fairly complete setup off of a car for a better look.