Budgeting /Planning for a trip to Miami/Key West

Going to a wedding down in Key West. I will spend a couple days in Miami with my cousin in Dade County near coral gables for a few days before heading to KW.

Marlins will most likely not be playing. What are some cool things to check out? It has been a while since I have visited any family that lives there, so I don't remember much. Any great places to get some food and drinks? South Beach for a day is on my list.

I'm also trying to throw together a budget. I don't want to break the bank, so realistically what should I expect to pay per day for food, drinks, and entertainment combined?