I've also been looking for parts to do this and ritebrew.com seems to have the best price I have found. They don't have a kit though so you'll have to order the parts individually. Kegconnection.com does have kits, and if you add kegs to the kits, they're like $32.50 per ball lock keg which is the lowest I've seen on the kegs.
I have no affiliation with either site, just passing on my findings.
I just completed my keezer. I bought some parts from Ritebrew and some from KegConnection. I was going to go with one of the kits from KegConnection but wanted Intertap Faucets.
I will say that the B grade kegs from KC are pretty beat up. The two I received were missing one handle, which they do mention on their site. I also ordered two kegs from Adventures in Homebrewing and those kegs were in much better condition and both handles were attached. They were cheaper but shipping was more.
The KC kegs are functional but with one handle missing it is a little difficult to move around.
I'm in the process of building my keezer, and I'd recommend piecing together your own setup to get exactly what you want. Lots of the kits come with inferior components. Shop around for the best deals, but I've got stuff off Amazon, Birdman Brewing, CHI company, and morebeer so far.
I ordered the bulkheads from the CHI CO. Most of my items came from Ritebrew. Faucets were $10 cheaper than other sites and as mentioned, wanted the Intertap flow controls.
The only thing I ordered from Amazon was the Taprite dual regulator. $10 cheaper than other sites. There was one site that was cheaper on the regulator but after factoring in the outrageous shipping it exceeded the cost of Amazon.
I agree with PADAVE, piece together your own parts. All sites will charge shipping so you will need to factor that into the cost. Kegconnection is the only site that has a flat rate shipping fee. They didn't have Intertap faucets which is why I ordered that item from Ritebrew.
Outside of the freezer, I think I spent close to $300 for everything I needed. If you are using the Bev Seal Ultra Tubing, make sure to use the John Guess fittings. Makes connections much easier and the tubing is cheaper through Ritebrew.
+1 for the mailing list route. I was pricing kits on Amazon, and had settled on a kit that seemed to be a really good deal. Then I got a holiday email for 20% off + free shipping from one of the major suppliers and ended up getting a 2 keg (new), dual regulator system for less than the 2 keg, single regulator with a "Y"system on amazon.