The fees for taking part in the Weetbix TRYathlon are too much of a hurdle for some families

More than 300,000 six-to-15 year-olds have taken part over the years...but at $50 a child the entry fee is too rich for some budgets.

Principal of Nelson's Hampden Street Primary School, Don McLean, says he doesn't understand why it's so expensive.

He says parents and educators are frustrated the event is heavily promoted, but not easily accessible.