Wholesale pricing to retailers for jerseys in Australia is around $100-110. The NRL earns a licensing fee from this amount and a percentage of this is then paid back to the clubs. If you buy from your club then they are earning the profit, and their portion of the licensing fee. If you buy from Rebel, they're only getting their portion of the licensing fee.
The fundamentals of supply and demand tell us that the market sets the pricing of the jerseys, in that retailers sell at a price where by they sell enough volume to consumers for them to be satisfied with volume and profit margin. If they make them too expensive, they won't sell volume. If they don't put enough margin on top, they don't make enough profit.
Comparisons to pricing in a different market (eg UK) is largely irrelevent because there are different influences on the market over there. For example, it is probably understood that RL is a "minor" sport in the UK so to encourage consumers to purchase merchandise the price point has to be set lower, by manufacturers and ultimately by retailers.
This presents a good opportunity for Australian consumers to purchase online from the UK at cheaper prices. If you do so, however, please remember that your club won't get as much revenue from this sale.
Most importantly, it has to be remembered that revenue is hard to come by for NRL clubs. As we know, most clubs struggle to break even each year. Merchandise is an important revenue stream, and the clubs need as much as they can get from it.
If you take anything away from this, if you make the decision to buy gear locally, please buy it from your club shop as opposed to Rebel etc as the club gets more out of it.