The machine that ends the ice runs.

By water volume, ambient temperature and how hard you run it. As a rule the chiller should be rated for continuous duty at your hottest month's ambient — that's the difference between holding 3°C in August and merely advertising it. Your quote sizes it against your actual tub and climate.

Comparable to a large refrigerator in steady state — the insulated tub does half the work by letting the compressor rest. Well-insulated setups typically land in the tens of dollars per month, not hundreds.

Yes — that's the designed upgrade path. Start with ice, and when the habit sticks, the chiller connects to the same tub and retires the ice runs permanently.