Typical oven element is 3KW. It runs for 10min to reach bake temp, then 2 min out of every 10 to maintain. Biscuits might take 12 min, or 1/5th of an hour. 1/5th x 3KW is 0.6KWh. A KWh costs (national average) 12 cents. 12c x 0.6 = 7.2 cents. $0.072 x 30 = $3. That's what it costs your uncle to make biscuits for a month.
Yes, smaller costs marginally less. But many utilities charge more than $3 taxes, fees or line charges having nothing to do with consumption.
What runs the electric bill up are things that draw kilowatts for HOURS. Like a fridge is just short of a kilowatt and runs roughly 12hr/day. That's 360KWh a month, x 12c = $43.20.
So you see, while an oven uses several KW, it seldom does so for more than a half hour. Whereas a fridge uses one KW, but does so for 12 hours. For a ratio of 1.5KW to 12KW or in very round numbers, the fridge uses 10 times as much just running as the oven does making biscuits. So it "almost doesn't matter" how efficient the oven is. It DOES matter how efficient the fridge is because it operates 24 times longer per day.