I think the OP was considering a chiller purchase as a back up to prevent an over heating disaster, since his wife has let the temperature rise to 89F a few times by mistake. I have a chiller on line for a similar reason - my AC system has failed in the last and I'm not willing to take a chance of ruining my tank when I can prevent it. It's saved me a few times over the years.
Chillers are not particularly expensive to run. A 1/10 hp unit which can cool 80g of water draws about 2.2 amps. That's going to cost about 2-3 cents per hour to run. A typical 1/4 hp chiller will cool up to 170g of water and draws about 3.0 amps. So now we're talking about 4-5 cents an hour to run. And keep in mind a chiller isn't likely to run all day and night either. (Consumption figures for AquaEuro chillers, electrical costs based on about 10 cents/kilowatt hour. My sympathies to Californians where this figure won't be accurate).
Chillers do produce heat. Every single electrical device ever made produces heat. But a chiller will still remain effective well into the 90Fs. The heat produced by 2-3 Amps of power draw is not significant.
It's true that chillers should not be operated in small, closed, unventilated cabinets. But if you don't want to run one outside of your stand cabinet, an under cabinet ventilation fan is usually easy & cheap to install and can easily keep the chiller compartment at the same level as ambient room temperature.
