The Bachelor of Communication Honours program uses the same 'funding model' as the Bachelor of Communication undergraduate courses. This means that there are a limited number of Commonwealth Supported Places (CSP) provided for local students, and so the costs you will incur are the same as you have during your degree. These places are limited and so entry is competitive - just because you have good enough results does not mean you will receive a place in honours if you apply.
For international students the same fee structure applies in honours as applies to RMIT Bachelor of Communication undergraduate programs. The same selection criteria applies for honours entry as applies to Australian applicants.