We stayed at the Radisson near the pier in Miami, was decent, nice pool and close to the pier, just a short taxi ride away. We used Priceline, you may want to give that a try to save some money.
DO NOT stay at the Ramada in Miami Beach.We stayed there last april and it was terrible,and dirty.Service was bad.When we returned home we filed a complaint.They gave us 50% refund.But it was not worth it.
You have to be very careful in Miami. I talked to someone who had property down there and we ended up staying at the Sheraton Four Points in South Beach right next door to Hilton's Fountain Bleu (5 Star Resort!). There was a boardwalk down the beach between the 2 properties and we went over to the Hilton and ate at their outside pool bar/restaurant. They were not at all crowded so they said we could use some lounge chairs and the pool and just ended up spending the afternoon there. We booked the Sheraton on hotels.com and it was very reasonable. A short and inexpensive cab ride to the port also. Check it out.