How much should it cost to service an old refrigerator?

[Will Collier]

We've got an old fridge in the garage that we use for, er, beverages. It's not cooling well any more, particulalry when the weather gets warm. How much should it cost me to get it serviced (I'm assuming it needs a freon charge)?

I have no idea how old it actually is, it came with the house. I'd guess at least 10 years, maybe more.