I think the best way to look at this is from a monetary perspective. You're obviously keen on Melbourne because of the courses better "status", and presumably the major reason for this is so you can get a better job when you graduate. Excluding other factors such as travelling, the basic question is will getting your Actuarial degree from Melbourne mean that, in the long term, you will earn a better salary then you would from Monash which will exceed the 6k a year you'll be saving from the scholarship? I can't answer that, but my cousin did Actuarial at Melbourne and assuming you get good grades, at this stage employers would PROBABLY see the Melbourne course as a better one which could in fact mean you'd have a greater potential to earn a better salary and thus bridge the gap.
Taking into account that Melbourne has a more accredited course which probably means less exams for you, probably has better lecturers and MOST LIKELY is more convenient to get to then Monash, I would personally choose Melbourne.