General
You will need:
1 x regulator,
1 x Pluto gun (or tap with panel adaptor if you want the tap in the door of the fridge this is more expensive though),
1, 2 is better kegs (post mix)
1 x beer quick connector
1 x gas quick connector
Gas line,
Beer line, and
CO2 (rented bottle).
As for the price all I can say here is shop around, get prices for the system as a hole and as individual parts. Try places that service pubs as well as HBSs. Watch ebay as you see parts sold there all the time I saw a two tap system and fridge go for around $400 recently.
To give you an idea there are pictures of my system here
http://groups.msn.com/MacabresBrewery/beerfridge.msnw you will not need all of this. Dogger has also put pictures of his here
http://www.homebrewandbeer.com/forum/viewtopic.php?t=1033 look for the link in the post from dogger. Evo has also put photos of his freezer on here somewhere.
As for the fridge running as a freezer Evo will tell you to run a chest freezer as a fridge. You will need to fix the thermostat or have beer popsicles.