Roger Clemens over his entire career hasn't broken $200M, if I'm not mistaken.  Considering someone better than Zito will get a better than Zito contract, its still rather impossible to get anywhere near a quarter million.  The first half of a pitcher's career (maybe even more, depending on injuries) is under the control of one team and an arbiter.  That doesn't leave much time to make up the remaining ground.

To compare, Roy Oswalt (5 years of service) had accumulated only $21M before he signed his big 5-year extension worth between 73 to 89 million dollars.  That would push his total up to just over $100M after 10 years.  How many years would he have left in him at that point?  He'd already be 34.  Another "benchmark" could be Dontrell Willis, who will have hardly accumulated $12M after this season (his fourth).

Inflation is ridiculous in today's FA market, but it's highly unlikely a pitcher will make much more than 1/4 of a billion (let alone 1/2) over his career.