The fans only cost about $0.30 - $1.00 but need to be purchased from the manufacturer in bulk (minimum order 100 typically).
Option 2 is take it down to your local PC store and get them to fix it. Chances are they won't have a replacement and there is the labor charge as well.
Finally now that the fan has failed and the card is over-heating there is a good chance the card has heat damage.
My opinion: Buy a new card. It will save you time and hastle if nothing else.