I wouldn't worry too much about that first chain failing at 90k without knowing the exact reason for the failure. Very unlikely that it was the chain that failed that early. More likely something else took the chain out, resulting in the $$$$ repairs. The best advice (as Sixto sez) is to check the elongation and go from there.

Replacing the timing chain is not normally a "preventative maintenance" thing like replacing the timing belt on later vehicles.

Sorry I can't tell you how much it would cost to replace the chain.....

Wes