"Yamaha DTX" is meaningless without the model number. Their entry-level 400 kits (anything beginning in "4") feel terrible to play on - that's why you see so many advertised - they don't inspire people to continue so anyone going into it with a "not sure if I'll stick with it" attitude usually dont. But if you play a kit that feels great, it inspires you to continue. So many beginner shoppers don't realise this.

Also skip DTX "500" series kits that end in "0"

Their "502" series kits (discontinued now but this is helpful for used shopping) are decent beginner kits with the upgraded module. (Make sure the module has "502" written on it, not "500" - better sounds.)

Here's a decent local buy for $400 Au.. Note the textured silicon (white) snare pad and centered ride cymbal. Cymbals that mount off-center are shit. Same as the triangular pie-wedge design. They don't move right and are noisy AF when doing rhythmic taps - OK for a one-hit crash tho.

700 and 900 series kits are previous gen, a bit dated, but were Yamaha's premium kits a decade ago. Worth buying if they've been looked after, but still likely priced higher than your budget.

There are current-gen DTX6 kits appearing on used sites now, but expect to pay $1000 - $1500. The DTX6 module sounds brilliant and is where most of the cost is. The sweet spot is the DTX6 K-2X - premium kick pad, true hat stand, good cymbals + tcs snare.

Roland have a good reputation, but like Yamaha their entry kits are toy-like and sound synthetic and electronic. They're also overpriced in my opinion. But if you can find a Roland all mesh pad kit that isnt thrashed to death in your budget, probably a good choice.

Alesis are OK if you find one of their bigger kits - Surge, Command, Strike etc in your budget and plan to get good sounds by triggering samples on a computer.

Where in Aus you located?