The two tanks I had fail were refurbished by a very good radiator shop. He told me the material in these tanks is not very strong, and particularly mounted to a high performance engine he warned they may develop pin holes, small cracks, etc and he was right.
the Kirkham tank is $500 now; I got it when they announced them and they had a special price available, can't remember how much exactly. See here:
Options and Accessories Info
The other nice thing about the Kirkham tank is the provision for the overflow line to a recovery tank as well as another port which connects to the top passenger side of the ERA radiator which helps greatly in purging air from the cooling system.