This year I have the use of my Dad's thermostatically controlled proppothingy.
Being mean broke early retired and on a pension I intend to use the propagator in the conservatory during the day as its warm there. At night, when environmental temperatures drop, I'll bring it into the house as it's warmer - providing it's not too heavy fully loaded. Hopefully this will help reduce running costs.
I'm told 1000w costs around 10p an hour if that's any help in calculating running costs.