If you look close at what is included, I can see where he has over $800 in it. Old beat up fridges with 1 cheap faucet go for $250 all day, but twin perlicks on a tower with 6 kegs?
Here's my conservative numbers.
Fridge $200 (sanyo mini fridge is more like $100 used, I have seen 4 between $50-100 over the past few years, got mine for $40).
Tower $100 (i have found 2 tower kits including tank for $100, tower by themselves $30-40)
2 Perlicks $80 (used they about $30)
Handles $10 (those are more like $2 a piece)
6 cornies $200 (spot on)
Regulator $ 40 (see tower)
5# tank $80 (see tower)
Drip tray $40 (see tower, since that is an after market those are $18)
At $500 this would be a steal.