Translation:The budget of this school is twenty million.
Rick is correct. Both Squiz and dkfour do not take the "ini" into account sufficiently.
THE school('s) budget: here the 's is more or less optional and the meaning hardly changes. With 'the' the imprecission can be disregarded wether it's "the budget" or "the school" that gets marked.
For "THIS" it is important to make sure you know what you are pointing out.
"This school budget": "This budget of a/the school".
"This school's budget": "A/The budget of this school"
The position of "ini" in the Bahasa sentence only allows the last version as a correct translation.