I'd have to say the agent has it right if it's advertised for weekly rent. Over the years if you paid weekly, what you'd end up paying is what the agent worked out.
However, you might be able to negotiate a deal for paying the month in advance (is there a bond as well?). You could either try bargaining or just pay weekly using direct debit or some such. If you've any debt (eg credit cards, loan etc) and are paying interest, you're probably going to be better off paying each week or week ahead rather than a month ahead. But I don't know if that's an option for you, and you'd have to do the sums.
