This has been beat to death and all the DYI will chime in for sure but bottom line you cant beat getting the kit from Kal. You will waste hours trying to find every part only to find you only saved a few bucks.
The short supply was a bunch of BS by MWS to get you to buy from them! You can find used ball lock kegs all over the place ranging from $28.95 and up. Dont drink the kool-aid from MWS and believe that crap!
Rant over... brew on.