I think he is trying to rob you blind mate, no way 5x for a round. Also do your maths, if he thinks he can do 600 on his own, they are either all very small, or he has priced them all very low and need to keep 600 of them for it to be worth while.
Have you asked him what is the likely sales from the customers he wants to sell and also, you will prob be better of sticking where you are than moving into another town to pick up the work, and keep your round compact.
For the price he is wanting you would be better of paying a canvasser, and you will get recently priced work in your area, that suits you for travelling.