Well iv finished mining now, Still holding on to a few BTC which ill sell if price ever gets back to $2X.XX.
My power billing is a bit like that.
Looking on last months bill I got so many KW/H charged at 0.19 then the last day it went up to tire 3 (high usage) which was charged at 0.29 but luckily it only cost $6 for that day but would of sucked being on that pricing for a week or 2. On the low rate it was only costing $2.XX per day about $15-16 per week for my rig and I was making $62NZD a week (when BTC was at $15USD.)

Was a good run tho. Managed to Pay off 1/4 of my 6850, 100% of my 6670 and buy 2X antec-kuhler-h2o-620 watercooler setups.
Both GFX cards are getting a good using with BFBC2 online now.

Just wish I had a time machine tho. Take my rig back in time with the GFX miner client to when bitcoin first started then I would have had sh*t loads of btc to sell when it was at the $2X.XX high.