Honestly, if I had read your email, I probably would have just assumed you meant your prize money for the last event. If you had said SERIES prize money, or season standings prize money, or some such, then I'd have known what you were asking about, but maybe that's just a nuance of American/British english. (On the other hand, was the person you were emailing a native english speaker?)
All that aside, was there a promise in 2005 to pay series standings prizes? I'd say that if there wasn't a promise in 2005, and Millenium was kind enough to pay out money at the end of 2005 anyway, that doesn't obligate them to repeat the favor a year later.