Depends on your budget, age and riding style.
Most of the entry level bikes from brands like Monty that retail around $700 are aimed at juniors so if you are older or more aggressive they might not do the job. Great for the right rider though.
If you are spending over $1000 then look at complete bikes from brands like Echo.
Second hand can be a good option for a beginner, they aren't always that common but if you check out the Australian section of
www.observedtrials.net you might find some good deals alongside a list of Australian importers and distributors.
Also search in this forum where a few beginners have previously asked some very good questions about starting out in trials.
Feel free to contact myself or any of the other people involved in the sport if you have questions.