At 500sq feet it's safe to say the bulk of your current electric and gas costs are to run your kitchen equipment. $16,000 a year.
So, $16,000 for your current equipment and assuming ALL of the electric and gas costs of the WFO places I have familiarity with is for heating/cooling their spaces (which it's not, they have walk-ins, coolers, etc), you are looking at about $45,000 per year in electric and gas for a space in the 3000 to 4000 sq ft range, assuming you are using the same amount of kitchen equipment as you currently are.
Is the larger space you are looking at going to have more equipment in the kitchen (larger coolers, etc)?. Assume that the electric and gas costs you are currently paying primarily for equipment doubles to $32,000 per year due to the increase in equipment in the new space. And still assuming the WFO places are spending all of their gas and electric costs on HVAC (which they are not), you're looking at $62,000 a year in gas and electric (using the most expensive annual gas and electric costs of the WFO joints I am familiar with).
So the $70k figure seems a little high, even when using the somewhat aggressive assumptions used above. Again, in your part of North Carolina that may be the going rate.