If price is the issue flying to MIA or FLL hiring a car and driving to Key West will be the cheapest choice almost every time. The drive is usually very pleasant also. The route is the easiest for navigation, I95 to US1, stop when Us1 ends, you are in Key West. The drive is about three hours or so, maybe 3 1/2 from FLL, and is full of small keys and entertaining causeways.