Working legally when you're not eligible in Australia?

You can't. The law is very strict here. You are better to save for your expenses before coming here.

I notice you mention the Work and Holiday Visa, but have you checked whether or not you can apply for the Working Holiday Visa. Go here to check it out - http://www.immi.gov.au/visitors/working-holiday/41...

If you aren't eligible for that, there are ways around it if you're a highly skilled worker, or if you can get an employer to sponsor you on your stay here, but as someone else said it's more likely that an employer would want you to stay for longer than a year in that case.

That said, there's no harm in checking around and asking. There's always talk of labour shortages in a number of industries, so you could look into that and see what's in demand. Then perhaps approach some employers and see what happens. Never hurts to ask.

Good luck with it!

If you're not eligible for a Work and Holiday visa, it is absolutely impossible to come for 3 months and work legally. You really will have to give up on the idea of working here or run a very real risk of deportation and exclusion. If you can't prove sufficient funds to cover your intended stay in Australia (something like AUD$9000+ for 3 months), you will NOT be allowed to even leave the airport and will be put on the first plane home at your own expense.

Work visas for Australia are restricted to people with qualifications and experience in occupations listed as being in need of workers. You must pass a points test; you must have acceptable qualifications and experience and you must meet English language, health and character requirements. If your occupation is not on the Critical Skills List (CSL), even if you meet all requirements, you will be waiting for years for a visa.

http://www.immi.gov.au/skilled/general-skilled-mig...

If you have employer sponsorship, no points test is required but everything else applies. Employer sponsorship is complex and expensive for an employer and there is no way you could hope to get sponsorship for such a short period.

http://www.immi.gov.au/skilled/skilled-workers/sbs...

You haven't mentioned what occupation you are in. There are certain occupations that would sponsor you, but not for only 3 months due to the red tape involved in obtaining such a visa.

The other option is working illegally. Despite Ozmaniac saying it is not common in response to a similar question, it is extremely common in Australia to do so. Just because you cannot see it does not mean it does not exist or is not possible. It exists mainly in the migrant communities where people from a common ethnic background run businesses and want to keep costs down as well as have people who fit in, or in industries such as commercial cleaning and apparel construction where English is not required (not that this is your problem at all).

The countryside is also a major source of illegal labour because those who are eligible to work will not do so because government benefits are more attractive than doing menial jobs.

You can be reported and deported as a result for working illegally, however this is usually due to a disgruntled ex-employee etc.