If the insulation is good, and you've stopped water evaporating the running costs are very low really. I put the power measuring thing on it and found that taking tap water up to 55°C took more power than running it at that temp for 3 days. I now use the hot tap, as the cold water tap is really damn cold at the moment.
I would say compared to the cost of a good sealer bag, which iirc was 12p for the 20x30cm, the electricity cost is quite low it shouldn't take 10kWh.
I have the Rubbermaid 11.4L Clear Space Saving Container with it's lid. When dremelling the whole I took great care so that it's an almost perfect seal against the plastic base of the Anova. It's not airtight, but it's certainly appears to be water tight even at 85°C. I put it on a bunch of rubber trivets, and leave it under the boiler, which is one of the naturally warmer spots of my flat.
Care should be taken to make a good "seal" on the top. Otherwise if you are doing a hot cook you will coat the ceiling or the kitchen unit above in condensation, not great.
I hear that the £5 "pan lid organiser" from IKEA does a great job as a separation rack. But I've yet to work up the courage to brave visiting IKEA!