Do you need it now? AiH runs sales on new 2.5 gallon kegs a few times a year, and they tend to run about $70-80 apiece. I just waited for a sale and pieced my system together. I started out with 4 new kegs, a new aluminum CO2 tank, cobra tap, fittings, an extra set of O-rings, plus a portable CO2 charger and extra set of CO2 canisters for it. I got it for just over $470 (including shipping). Plus I got another $20 worth of reward points, which I put towards the next keg sale they ran.
Needless to say, if you aren't in a huge rush, the subscribe to AiH's newsletter and jump when they run their next sale. You can score a much better deal there.