Its hard to give you an answer as we used our credit card for the big ticket items (train tix can be bought with credit card). It depends on what you plan on doing. If you are planning on getting a private tour guide for the day you will need more (maybe twice that). If you plan on taking trains, buses and taxi's $200 is ok IF you use your credit card for entrance fees to the museums and such.
Carnival Cruise Lines:
Fantasy 90, Celebration 95, Victory 05, Conquest 05, Spirit 6/06, Freedom 6/08, Holiday 7/08, Victory 6/09, Valor 9/09, Dream 6/10, Splendor 8/10,Conquest 8/11,Magic 11/11,Triumph 4/12,Spirit 7/12,Freedom 11/12, Triumph 2/13 - The fire cruise
NCL Dream October 2006, RCCL Mariner OTS June 2007