The kegs that come in those kits are the exact same thing as what you are looking at in your LHBS, and I highly reccomend replacing all o-rings no matter if they leak or not. If you don't, you'll regret it when your tank is empty and your beer is flat. $20 is a good price, so snag up a couple, maybe four. The rest of the equipment can be found on ebay, northern brewer, Austin Homebrew, etc. all for about the same prices. Do some thinking about how many kegs you want hooked up at one time, and consider whether or not you want two different CO2 pressures in the system before you buy anything. Design the system first, then start buying. That way you don't waste any moolah.
A great man knows that he knows NOTHING