Is it compulsory that you hire a van for £150 a week, could you not use your own van?
It might sound like hard work but what you described would probably suit some people, especially folk in low paid jobs. £600 a week driving around and without a boss on your shoulder would be ideal.
We looked into it at work awhile back as we have a small fleet with irregular workload and from what I recall it was just that the van has to be upto a certain standard - which if you don't have a van of that standard will cost you about that a week to hire.