Years ago, dive tables were the standard. Today, most divers wear a personal dive computer and they should.
The computer tracks depth, time, ascent rate, and no-deco limits in the moment. Dive tables are a fixed calculation. If you move between depths partway through, it updates. Tables don't.
Wrist-mount computers are the most common go for these days. They're small enough, readable underwater, and you'll use them as a daily watch as well. Hose-mounted computers are an option but fewer divers pick them now.
Entry-level computers go for around $250-400 and do everything the average diver requires. You get depth tracking, bottom time, no-deco limits, a logbook, and often an entry-level freedive function. The $500-800 range adds transmitter compatibility, improved screens, and additional nitrox options.
The one thing new divers don't think about is conservatism settings. Some computers are more cautious than others. A tighter setting gives you shorter bottom time. More aggressive algorithms extend time but at reduced safety margin. Neither is wrong. It just your style and your diving background.
Talk to people at a local dive store who uses various models before you decide. Good dive stores will have real-world feedback on what works versus what's marketing. The better Cairns dive stores publish gear reviews and honest reviews find more info on their sites too