Look in the Classifieds
The List?n Diario has a large classified section and the last part is for "Varios" Sometime there are fridges thee.
Also keep your eye out for the auctions at the US embassy. The have fridges and other household goods at very fair prices.
If you come to Santiago, you should be able to find a used fridge for a reasonable price. Let me know if you want me to ask around a bit.
HB