To answer you question about what to charge, is dependent on experience as well as location. Your location could warrant a high fee such as $100 per hour, but that all depends on experience and skill level. As an artist starting out, I would charge between $30 and $50 per hour, with $50 an hour being the preferred rate. Use our pricing guides and plug in your hourly rate. You should also time yourself on a regular basis to see how much time it takes to do a project. By the way, never sell yourself short. If it takes you 5 hours to do a brochure, and you know that most designers would take 10, then charge for 10. If the client has a hard time with the costs, go down to 8 hours charge. You’re still making money and are beating the competition.
As a guide to pricing comps, I normally charge full design rate. The reason being, is a comp takes as long as the final art in most cases. The idea, creative direction and set up is all in place even when designing a comp. As for spec work, that is always free. I do not recommend ever doing spec work unless you feel that you stand a chance to get the job. Chances are that the prospective client will take your idea and take it someplace else for cheaper. About 98% of the time, I do not touch spec work. If I feel lucky or I know I could get the job, I will do a job on spec. As for an hourly rate to charge, that will all depend on your skill level. I bill between $60 and $100 an hour for design or comp work. My suggestion is to never go below $50 an hour; you have to run a business and anything less will not pay the rent. For some ways to protect your work, you will need a contract, and possibly a copyright ownership agreement.
As for the rate of $125 per hour sounds fine. By looking at a currency converter, your $125 an hour rate is about equal to $77 per hour here in the USA. However, I would suggest calling up a few local design firms and do a little price checking. Also, depending on the Australian economy, will depend on how much you can charge. You might even consider having 2 rates, one at your regular rate and the other a little lower for lesser budget clients or bad economy issues. I have my rates between $60 and $100 US dollars per hour which would equal to about $97 to $162 AUD.