Across the Hampshire or Berkshire borders, each pupil attracts more than pound;100 more a year than he receives as a secondary school head in Wiltshire.
"You're constantly frustrated," he says. "There is a lot you want to do for the youngsters here that you simply cannot do. It means a lot of time spent looking at balancing the books instead of focusing on teaching and learning."
Wiltshire's education standard spending assessment - the amount Government thinks it should spend - is below the national average for shire counties. But Mr Trobe hopes the Green Paper's pledge to "level up" funding for authorities will ease his problems.
Malmesbury school this year received its first real-terms funding inrease in Mr Trobe's nine-year tenure: pound;2.65m before the standards fund and Gordon Brown's Budget hand-out. But he still feels he cannot confidently plan ahead. The paper offers hope that soon he will be able to.
But he is dismayed that there may be no compulsion on local authorities to pass money on. His sixth-form has received no extra money for the additional courses students are taking this year - despite Government claims it has put pound;35m in nationally.
And he thinks ministers have fudged a fundamental issue - the balance of funding between primaries and secondaries, which, despite the proposed national funding entitlement, will still be decided by local authorities.
"I am optimistic that the Government will tackle these problems," he says. "But I want to see exactly how much money this is going to mean - how many years is it going to take to level up?"