It all comes down to what its worth to you, although £65 or half a lamb is pretty fair considering its so close by.
Worst thing would be having to see someone else's sheep there every morning from the bedroom window knowing you then have to travel to check yours (there is the cost saving).
Look after the paddock well by pulling out thistles and docks, maybe strim around the edges and catch the odd mole if your able.
That's always worked well for me and I've usually been given the ground for the time I have the sheep on and certainly asked back. Some people might say that's too much in the way of effort after all you are paying for it but land is getting harder to find in some areas especially on your doorstep.