I want to rent a Porche 911 Convertabile for my dad for christmas.
Where can i find a dealer willing to do this within 50 miles of
Cochran, GA 31014? I would like to rent it for at least 2 days but no
more than 4. I would not like to pay more than $200.

There are two problems here,

1) Finding the car rental in your area,
2) Finding one that would rent the car for $100 or less/day.

I think it might be possible to find a car, but even if you did, there
is no way a luxury car rental place would rent the car for $100/day.
Maybe you could work something out with a Porsche dealer, but I doubt
that deal would be advertised....

There are "exotic" car rental businesses that rent this type of
specialty car, but nowhere near the prices you are willing to pay. 
Also, a dealer is not going to let you borrow a new car that he is
trying to sell new.