I'm coming in late on the this thread but...
1) 200$ shipping a piece is only 50$ less than the individual shipping cost. I've purchased 2 from Ken.
2) Have you contacted Angela at Sega ( segaarcade.com )? I've purchased various parts from her before, they get them from sega logistics in Japan. Maybe she could help you get a arrange for container full of used cabs from japan for a REAL discount. Ken can't make you any volume discounts since that's how he makes his money.
3) if you go look at prices for cabs on YAJ, you'll realize how cheap used cabs are over there. the yen is strong but arcades are on the decline in Japan , therefore used cabs are flooding the market. 60 cabs is a lot but if you can get them here ( shipped) for 1/2 the price ken sells them, you should be able to find 60 buyers across all the arcade forums.
http://page2.auctions.yahoo.co.jp/jp/auction/b132818851
http://page16.auctions.yahoo.co.jp/jp/auction/u39784799
http://page18.auctions.yahoo.co.jp/jp/auction/w70799386
http://page8.auctions.yahoo.co.jp/jp/auction/h159543602
....
All and all, it's a complex and expensive operation. Have you talked to anyone with group buy experience ?