How much does 12 volt power converters cost?

They all vary in price. you can get one that will run a small fan for $50.00, or one that will run a refrigerator for upwards of $500.00 You really have to shop around for them. Plain and simple, if it is kind of small, like the size of a car radio, it will not do much. If it is huge like about 1 foot wide by 2 feet long, it is a MONSTER!!! will power anything. Hope this helps!!