Zip on over to Best Buy or even on fleabay and pick yourself up an under $ 100.00 gaming card.
Just get one with at least 128MB of memory. You can still pick up an Nvidia GF Ti 4400-4600's for under $100.00 on ebay. Not a bad card still. Any ATI's will work as well.
You really dont need a $ 4000.00 card to run AC9 imho.
Have a decent processor and plenty of ram.