Just a gentle warning - the 457 is an employer-sponsored temporary visa. The employer does not have to offer any sort of relocation package, that is something that is negotiated between employer and employee. It does not give an automatic right to apply for PR either - that is entirely dependent upon your employer being willing to support your application. The maximum time that it can be granted for is 4 years but again that is decided between your prospective employer and DIAC, it can just be granted for 1 year - it is dependent upon what is written in to your employment contract as the term fo your employment. If you want to leave your employer during the validity of your visa (you don't like the job, your location etc) then you have just 28 days to find another employer sponsor or you will have to leave the country.
As a nurse you can apply offshore for a 175/176 permanent residency visa, as nursing is a skills shortage employment. Although this can take longer to get, it does give you permanent residency immediatley, with the benefits that confers - subsidised medical care (Medicare), access to free/ subsidised schooling and education, access to some social security benefits, no restrictions on where you live (if you apply for a state-sponsored 176 then you have to live there for 2 years) or the employment that you take.
Charges for AHPRA registration are AU$160 annually. However, initially you have to pay an assessment charge, an application fee and a registration fee, totalling approx AU$540.
The whole process is a minefield and it is worth getting some information from a registered migration expert - most offer a free information session. If you really want to get started on the process then it is advisable to get your AHPRA registration submitted and for your OH will need to get a skills assessment done by the appropriate body for his job. These are the things that usually take the longest to get sorted.
Good luck with it all and hope that we will all get to Oz eventually