I think you have to weigh up how much $30,000 means to you/your parents, how much benefit you think you'll derive from Crimson over more affordable options, and whether you want to study med at Oxbridge at all costs.
I don't know much about Crimson but personally, I've never been in a position to pay that amount for a tutoring or mentoring service, and I think that a lot of the preparation can be done independently with enough dedication. Paying more doesn't necessarily guarantee a better service and there are surely UCAT tutors or programs around that are priced more reasonably.
Perhaps you could try searching for current UK medical students or recent graduates who could guide you through the preparation? A quick search for BMAT past papers yields
https://www.admissionstesting.org/for-test-takers/bmat/preparing-for-bmat/practice-papers/ and one of the best ways I've found to approach exams is to do past/mock questions, with attention to identifying and rectifying weaknesses. Similarly, there'd surely be more affordable independent tutors who could prepare you specifically for a UK med interview.
If you're affluent enough to afford Crimson without sacrificing anything else - that's your choice, but I think there are better uses for that amount of money.
At some point, also consider (assuming you are Australian domestic):
- The cost of being an international medical student
https://www.ox.ac.uk/admissions/undergraduate/fees-and-funding/course-fees- Whether you want to stay and practise in the UK - overseas qualified doctors returning to Australia generally need to pass additional assessments
- Whether you're certain you want to move away from home for at least a few years, and whether you're sure about the UK specifically. Having been on exchange, I found that the mental impact of being away from friends and family was something I really hadn't considered properly before deciding to move. There's also the financial aspect of living at home vs paying rent.
- How much med at Oxbridge means to you - does that outweigh the advantages of studying med domestically? We do have some excellent medical schools too!