Depends on the nature of the leak. The worst kinds are those that require the transmission to be removed because of leaky seals at the end bearings.
The greatest cost is obviously the labor which is now at $100/hr.
You are looking at a 17 year old car for which it becomes problematic to pay a large repair bill, because at that age things will continuously require repairs.
If you can afford to make a small monthly payment, I would say go get a new reliable inexpensive car with a good warranty. I believe some of the Korean cars offer that and are getting quite good in quality as well.
Remember, it is just my opinion. Good luck.