Hi Gav - if your brother is fishing 300-500g jigs, then he is jigging deep water and you will need equipment that is at least able to stand up to the rigours of being able to constantly retrieve jigs of that weight. I'm probably one of the worst jiggers in the world but I think I can at least give you some idea on what might be suitable within an acceptable price range.
you'd probably be wanting to fish PE6-8 class so I have a few suggestions below:
Most of the seasoned jiggers here use Shimano Stella 20000 or Daiwa Saltiga 6500 Expeditions. These reels are specially made to take the rigours of deepwater jigging but are very expensive, ranging in price from about $1200 - $1500. That said, you don't need to spend money of this magnitude especially if you're just starting off the sport. Two reels you could consider are the Shimano Spheros and Saragosa in the 18000 size. These reels are much cheaper than their stablemate, the Stella. i think you wil find these ranging from about $280 to $400. Both of these reels are capable and have been designed to handle the drag pressure necessary ot extract big tough fish from the depths.
In terms of a rod, again, if you're look at the premium end of the market, there are rods for frightening prices. You don't need to spend that kind of money though and a couple of excellent rods you could look at include the Shimano T-Curve 400. This rod can be had for around $350 and is an terrific rod for the price. It will match up well with the Saragosa or Spheros. A Daiwa Monster Mesh 582XHB would also be suitable and can be had for around $300.
You should be able to put an outfit together for $600 to $700 which is less than the price of a second hand Stella or saltiga.
By the way, if you haven't jigged before, stick to the lightest jigs you can get away with. For me, a 500g jig makes a nice paper weight. Why would anyone with any common sense want to drop half a kilo down 120m and reel it back up again!?
of course, there is nothing wrong with casting a 250g popper and reeling it back..........